pip - eventlet doesnt support dnspython >=2.3.0 (Fixes build error)

requirements.txt

@@ -22,6 +22,12 @@ chardet>2.3.0
 wtforms~=3.0
 jsonpath-ng~=1.5.3
 
+
+# dnspython 2.3.0 is not compatible with eventlet
+# * https://github.com/eventlet/eventlet/issues/781
+# * https://datastax-oss.atlassian.net/browse/PYTHON-1320
+dnspython<2.3.0
+
 # jq not available on Windows so must be installed manually
 
 # Notification library