Fixed missing package reference

Caused this exception before:

```
/home/pascal/Projects/javascript/yeoman/generator-boilerplate/app/index.js:12
.writeln('Generating from ' + 'Generator Boilerplate'.cyan + ' v' + package.ve
                                                                    ^
ReferenceError: package is not defined
    at module.exports [as exec] (/home/pascal/Projects/javascript/yeoman/generator-boilerplate/app/index.js:12:79)
    at next (/home/pascal/.npm/lib/node_modules/yo/node_modules/yeoman-generator/lib/base.js:275:18)
    at run (/home/pascal/.npm/lib/node_modules/yo/node_modules/yeoman-generator/lib/base.js:289:4)
    at Environment.run (/home/pascal/.npm/lib/node_modules/yo/node_modules/yeoman-generator/lib/env.js:424:20)
    at init (/home/pascal/.npm/lib/node_modules/yo/bin/yo:68:7)
    at pre (/home/pascal/.npm/lib/node_modules/yo/bin/yo:81:3)
    at Object.<anonymous> (/home/pascal/.npm/lib/node_modules/yo/bin/yo:105:1)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
```