Add repository to package.json.

Using the latest jquery-boilerplate, when I do an "npm install", I get the following warning:

```
npm WARN package.json boilerplate@0.1.0 No repository field.
```

This pull request adds a repository field to package.json, fixing that warning. 

The repository field is specified the canonical way (as per https://npmjs.org/doc/json.html) for a git repo.