Publish builds to S3.

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

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