URL generation endpoint returns plain text, but Content-Type header is "application/json"

Calling the content/slugs endpoint as described in CHANNELMGR-1483, the endpoint works and returns the expected result.

However, since the response header "Content-Type" indicates "application/json", AngularJS' $http service expects a JSON string and tries to parse it. This causes an error.

To fix this, the Content-Type header should be set to "text/plain".

HTTP/1.1 200
Date: Fri, 27 Oct 2017 10:35:19 GMT
Content-Type: application/json
Content-Length: 13