Revert exception message

Author: Luke Bakken

riak/codecs/ttb.py

@@ -181,7 +181,7 @@ def decode_timeseries(self, resp_ttb, tsobj,
                 raise RiakError(
                     "Expected 3-tuple in response, got: {}".format(resp_data))
         else:
-            raise RiakError("Unknown TTB response type: {}".format(resp_ttb))
+            raise RiakError("Unknown TTB response type: {}".format(resp_a))
 
     def decode_timeseries_cols(self, cnames, ctypes):
         cnames = [bytes_to_str(cname) for cname in cnames]