Fix tox

Author: methane

tox.ini

@@ -9,6 +9,7 @@ setenv=
 deps=
     pytest
 
+changedir=test
 commands=
-    c: python -c 'from msgpack import _packer, _unpacker'
-    pure: py.test test
+    c: python -c 'from msgpack import _packer, _unpacker' && py.test
+    pure: py.test