Adds docs.google.com/feeds to default OAuth scopes

When using OAuth, it's apparently now necessary to pass an additional scope to the JWT auth request:
`https://docs.google.com/feeds`

Without it, requests for spreadsheet data 404, yielding downstream errors like:
```
TypeError: Cannot read property 'feed' of undefined
  at /your-app/node_modules/edit-google-spreadsheet/lib/index.js:421:15
```

Caveat: I have not seen any documentation from Google about this change. It is possible that it's unintended on their part. At the moment, their own [OAuth Playground](https://developers.google.com/oauthplayground/) returns 404s for spreadsheet API requests built with the wizard –  unless you manually add the `https://docs.google.com/feeds` scope.

![screen shot 2014-04-30 at 9 58 04 am](https://cloud.githubusercontent.com/assets/141130/2842043/d918c550-d06f-11e3-9747-bb735aee91a2.png)



See also this [stackoverflow thread](http://stackoverflow.com/a/23385092) from the past 12 hours.