Fix for detecting application/json payloads

Firefox wouldn't allow updates to items.  They would POST ok, but PUTs
would always return a 404.  Reason was chrome was sending the normal
"application/json", but Firefox was sending "application/json;
charset=UTF-8".

This commit looks for the PRESENCE of applicaiton/json in the request
content type instead of the entire content_type being application/json
Merge pull request #1 from groovetrain/master

Fix for detecting application/json payloads