Publish builds to S3.

This will publish builds to S3 to the following URL's:

```
<S3_FILE_PREFIX>/ember-easyForm.js
<S3_FILE_PREFIX>/ember-easyForm.prod.js
<S3_FILE_PREFIX>/ember-easyForm.min.js
<S3_FILE_PREFIX>/daily/<YYYYMMDD>/ember-easyForm.js
<S3_FILE_PREFIX>/daily/<YYYYMMDD>/ember-easyForm.prod.js
<S3_FILE_PREFIX>/daily/<YYYYMMDD>/ember-easyForm.min.js
<S3_FILE_PREFIX>/shas/<SHA>/ember-easyForm.js
<S3_FILE_PREFIX>/shas/<SHA>/ember-easyForm.prod.js
<S3_FILE_PREFIX>/shas/<SHA>/ember-easyForm.min.js
```

The following secure environment values need to be added to
`.travis.yml`:

* S3_ACCESS_KEY_ID
* S3_SECRET_ACCESS_KEY
* S3_BUCKET_NAME - Pre-populated to `builds.dockyard.com`
* S3_FILE_PREFIX - Pre-populated to `ember-easyForm`