Do not always add a .json. Look if we already have one somewhere instead.

For some calls, for example "search user", you need to perform a call that look like that :
  /api/v2/users/search.json?query={query}
the .json is already there, but not at then end, therefore this will result a call like that
  /api/v2/users/search.json?query={query}.json

We need to prevent that to happen.
Merge pull request #1 from Haza/master

Do not always add a .json. Look if we already have one somewhere instead.