Add dependency for newrelic.coffee

Otherwise I can't run local hubot

```
DEV banyan ☁  ./bin/hubot
Hubot> [Wed Jul 02 2014 22:57:30 GMT+0900 (JST)] WARNING The HUBOT_AUTH_ADMIN environment variable not set
[Wed Jul 02 2014 22:57:30 GMT+0900 (JST)] INFO /Users/banyan/quipper/quipper-hubot/scripts/assign.coffee is using deprecated documentation syntax
[Wed Jul 02 2014 22:57:30 GMT+0900 (JST)] INFO /Users/banyan/quipper/quipper-hubot/scripts/media.coffee is using deprecated documentation syntax
[Wed Jul 02 2014 22:57:30 GMT+0900 (JST)] INFO /Users/banyan/quipper/quipper-hubot/scripts/ps.coffee is using deprecated documentation syntax
[Wed Jul 02 2014 22:57:30 GMT+0900 (JST)] INFO /Users/banyan/quipper/quipper-hubot/scripts/resque.coffee is using deprecated documentation syntax
[Wed Jul 02 2014 22:57:30 GMT+0900 (JST)] INFO /Users/banyan/quipper/quipper-hubot/scripts/smoke.coffee is using deprecated documentation syntax
[Wed Jul 02 2014 22:57:31 GMT+0900 (JST)] ERROR Unable to load /Users/banyan/quipper/quipper-hubot/node_modules/hubot-scripts/src/scripts/newrelic: Error: Cannot find module 'xml2js'
  at Function.Module._resolveFilename (module.js:338:15)
  at Function.Module._load (module.js:280:25)
  at Module.require (module.js:364:17)
  at require (module.js:380:17)
  at Object.<anonymous> (/Users/banyan/quipper/quipper-hubot/node_modules/hubot-scripts/src/scripts/newrelic.coffee:25:10)
  at Object.<anonymous> (/Users/banyan/quipper/quipper-hubot/node_modules/hubot-scripts/src/scripts/newrelic.coffee:25:1)
  at Module._compile (module.js:456:26)
  at Object.loadFile (/Users/banyan/quipper/quipper-hubot/node_modules/coffee-script/lib/coffee-script/register.js:16:19)
  at Module.load (/Users/banyan/quipper/quipper-hubot/node_modules/coffee-script/lib/coffee-script/register.js:45:36)
  at Function.Module._load (module.js:312:12)
  at Module.require (module.js:364:17)
  at require (module.js:380:17)  at Robot.loadFile (/Users/banyan/quipper/quipper-hubot/node_modules/hubot/src/robot.coffee:216:9)
  at Robot.loadHubotScripts (/Users/banyan/quipper/quipper-hubot/node_modules/hubot/src/robot.coffee:243:8)
  at /Users/banyan/quipper/quipper-hubot/node_modules/hubot/bin/hubot:99:30
  at fs.js:271:14
  at Object.oncomplete (fs.js:107:15)
```