Limit the permissive CORS headers to JSON
Limit the permissive CORS headers to JSON

As noted by @zeridon, the CORS headers of the UsersController#present
action were too permissive. Limit cross site requests only to the json
format on this method. This fixes #28.

user890104/fauna,user890104/fauna,initLab/fauna,initLab/fauna,user890104/fauna,initLab/fauna