Also update pyyaml in test requirements.
@@ -18,7 +18,7 @@ nose-timer>=0.7.4,<0.8
# splitting tests run on a separate CI machines
nose-parallel==0.3.1
# Required by st2client tests
-pyyaml<4.0,>=3.12
+pyyaml==4.2b4
RandomWords
gunicorn==19.7.1
psutil==5.4.5
