Json decode only responses with json content type

When I wanted to get code of JSON file (that exists in repository) using blob API method, I got parsed JSON, but I wanted plain text...
Url: projects/<project id>/repository/commits/<sha>/blob?filepath=<some json file>
'$this' is better than 'parent'
Merge pull request #44 from schneidermichal/master

Json decode only responses with json content type