Replace underscore by lodash

Summary:As far as we agreed to merge `rnpm` into react-native core, we need to align our dependencies to exclude duplications. One of the steps forward would be to use the same utilities library. According to the thread on fb, everybody is fine with replacing underscore by lodash (which we use internally for rnpm).

So, here we go!

cc mkonicek davidaurelio grabbou

**Test plan**
```
$ npm test
```
![image](https://cloud.githubusercontent.com/assets/2273613/13173972/ee34c922-d700-11e5-971b-68ff7322b6d6.png)

**Code formatting**

Changes are aligned with the current [style guide](https://github.com/facebook/react-native/blob/master/CONTRIBUTING.md#style-guide).
Closes https://github.com/facebook/react-native/pull/6030

Differential Revision: D3016271

Pulled By: davidaurelio

fb-gh-sync-id: c4f6776a7de7470283d3ca5a8b56e423247f5e45
shipit-source-id: c4f6776a7de7470283d3ca5a8b56e423247f5e45

packager/react-packager/src/SocketInterface/__tests__/SocketInterface-test.js

@@ -10,7 +10,6 @@
 
 jest.setMock('uglify-js')
     .mock('child_process')
-    .dontMock('underscore')
     .dontMock('../');
 
 var SocketInterface = require('../');