Add --compiler python3.4 option to run_tests.py
diff --git a/tox.ini b/tox.ini
index a655935..66b74a3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,7 @@
 # GRPC Python tox (test environment) settings
 [tox]
 skipsdist = true
-envlist = py27
+envlist = py27,py34
 
 [testenv]
 setenv =