Allow a lower patch version of dateutils (#4)

Author: vmandke

setup.py

@@ -24,7 +24,7 @@
         'requests>=2.9.1, <3.0',
         'jsonpickle>=0.7.1, <1.0',
         'cachecontrol>=0.11.7, <1.0',
-        'python-dateutil>=2.5.3, <3.0',
+        'python-dateutil>=2.5.1, <3.0',
         'enum34>=1.1.6',
         'lxml>=4.3.4'
     ]