change assert for python 2.6 compat

Author: maikthomas

tests/test_token_generation.py

@@ -67,7 +67,7 @@ def test_generate_data_token(self):
     def test_generate_no_data_token(self):
         token = self.opentok.generate_token(self.session_id)
         assert isinstance(token, text_type)
-        self.assertNotIn(u('connection_data'), token_decoder(token))
+        assert u('connection_data') not in token_decoder(token)
         assert token_signature_validator(token, self.api_secret)
 
     @raises(TypeError)