fix(user): change to throw useful exception

Currently, when a user hits the /users/<username>/suggested route, a large exception is thrown
in the logs since this route is not implemented. A NotImplementedError would be more useful for
the time being.

Resolves umermansoor#4

Author: griffinb

services/user.py

@@ -82,7 +82,7 @@ def user_suggested(username):
     :param username:
     :return: Suggested movies
     """
-    pass
+    raise NotImplementedError()
 
 
 if __name__ == "__main__":