Properly set up the JSONP file

Currently, the JSONP file requested by http://brackets.io has no callback and can't be executed therefore.
This is being fixed with this PR.

The easier solution would be to set the [Access-Control-Allow-Origin](https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS#Access-Control-Allow-Origin) header on S3.