Use rawgithub.com to get files with the right mimetype

When loading the page in chrome, I saw the following error:

Refused to execute script from
'https://raw.github.com/jfhovinne/jFeed/master/src/jfeed.js' because its
MIME type ('text/plain') is not executable, and strict MIME type
checking is enabled.

Switching the urls to rawgithub.com transfers them with the proper
mimetype and removes these error messages