Use mock on py27, builtin mock on py33+.

tests/_compat.py

@@ -0,0 +1,8 @@
+import sys
+
+PY2 = sys.version_info[0] == 2
+
+if PY2:
+    import mock
+else:
+    from unittest import mock

tests/test_client.py

@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 import pytest
-from mock import Mock
+from _compat.mock import Mock
 
 from tinyrpc.exc import RPCError
 from tinyrpc.client import RPCClient, RPCProxy

tests/test_dispatch.py

@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
-from mock import Mock, MagicMock
+from _compat.mock import Mock, MagicMock
 import pytest
 
 from tinyrpc.dispatch import RPCDispatcher, public