fixed urllib3 on version 1.17 until 1.19 is released with this fix: urllib3/urllib3#987 (1.18 was breaking travis)

Author: Callum Oakley

setup.py

@@ -35,7 +35,7 @@
     install_requires=[
         'six',
         'requests>=2.3.0',
-        'urllib3',
+        'urllib3==1.17',
         'pyopenssl',
         'ndg-httpsclient',
         'pyasn1'