Content-Type should specify charset for JSON responses

UTF-8 is indeed the default, but this prevents encoding issues in Webkit browsers. 

"JSON text SHALL be encoded in Unicode. The default encoding is UTF-8."
http://www.ietf.org/rfc/rfc4627.txt
Merge pull request #197 from HowToMeetLadies/patch-1

Content-Type should specify charset for JSON responses