Upgrade eventlet to the latest stable version.
greenlet==0.4.13
# Note: 0.20.0 removed select.poll() on which some of our code and libraries we
# depend on rely
-eventlet==0.22.1
+eventlet==0.23.0
gunicorn==19.8.1
kombu==4.1.0
# Note: amqp is used by kombu
