Updated package.json to include mocha.

In package.json, added mocha as a dependency when using node to test. 
If this generator was used without mocha installed globally the test would fail to run.


###Before
```javascript
  "dependencies": {<% if (environment === "Node") { %>
      "chai": "~1.8.0"
```
###After
```javascript
  "dependencies": {<% if (environment === "Node") { %>
      "chai": "~1.8.0",
      "mocha":"2.0.1"'''
```