Removed unused exception class (#233)

Author: Roach

slackclient/server.py

@@ -251,10 +251,6 @@ def api_call(self, method, timeout=None, **kwargs):
         return self.api_requester.do(self.token, method, kwargs, timeout=timeout).text
 
 
-class SlackCongigurationError(Exception):
-    pass
-
-
 class SlackConnectionError(Exception):
     pass