fix broken test for 'fast' mode

`npm test` fails currently. below is log from [Travis CI](https://travis-ci.org/lauterry/generator-ngtailor#L1562)

```bash
  1) fast package.json content:
     Uncaught AssertionError: package.json did not match '/"name": "generator-ngtailor"/'.
      at /home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/test/assert.js:146:12
      at Array.forEach (native)
      at Function.assert.fileContent (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/test/assert.js:141:9)
      at RunContext.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/test/test-mode-fast.js:67:11)
      at RunContext.emit (events.js:92:17)
      at g (events.js:180:16)
      at emit (events.js:117:20)
      at null.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/base.js:364:10)
      at null.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/base.js:372:5)
      at Queue.g (events.js:180:16)
      at Queue.emit (events.js:92:17)
      at Queue.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:68:12)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:79:43)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at Queue._exec (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:83:3)
      at null.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/base.js:428:7)
      at Conflicter.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/util/conflicter.js:70:5)
      at /home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/async/lib/async.js:254:17
      at /home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/async/lib/async.js:157:25
      at /home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/async/lib/async.js:251:21
      at Object.callback (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/async/lib/async.js:615:34)
      at null.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/base.js:656:21)
      at processImmediate [as _immediateCallback] (timers.js:345:15)
  2) fast app.js content:
     Uncaught AssertionError: app/js/app.js did not match '/angular\.module\('generator-ngtailor'/'.
      at /home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/test/assert.js:146:12
      at Array.forEach (native)
      at Function.assert.fileContent (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/test/assert.js:141:9)
      at RunContext.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/test/test-mode-fast.js:159:11)
      at RunContext.emit (events.js:92:17)
      at g (events.js:180:16)
      at emit (events.js:117:20)
      at null.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/base.js:364:10)
      at null.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/base.js:372:5)
      at Queue.g (events.js:180:16)
      at Queue.emit (events.js:92:17)
      at Queue.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:68:12)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:79:43)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at SubQueue.run (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/subqueue.js:41:45)
      at Queue.next (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:80:39)
      at Queue._exec (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/grouped-queue/lib/queue.js:83:3)
      at null.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/base.js:428:7)
      at Conflicter.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/util/conflicter.js:70:5)
      at /home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/async/lib/async.js:254:17
      at /home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/async/lib/async.js:157:25
      at /home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/async/lib/async.js:251:21
      at Object.callback (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/node_modules/async/lib/async.js:615:34)
      at null.<anonymous> (/home/travis/build/lauterry/generator-ngtailor/node_modules/yeoman-generator/lib/base.js:656:21)
      at processImmediate [as _immediateCallback] (timers.js:345:15)
npm ERR! Test failed.  See above for more details.
npm ERR! not ok code 0
The command "npm test" exited with 1.
```

this PR is for fixing this problem:smile:
In order to update the value of `currentWorkingDirectory` every when `NgtailorGenerator.init` called, I changed like this