Dropping support for py35

As per below ML thread, we are good to drop the py35
support now:
http://lists.openstack.org/pipermail/openstack-discuss/2019-April/005097.html

[1]http://lists.openstack.org/pipermail/openstack-discuss/2019-April/004647.html
[2]
https://governance.openstack.org/tc/reference/runtimes/stein.html
https://governance.openstack.org/tc/reference/runtimes/train.html

Change-Id: Icf0980b8f1a8d884b05621f5298c13cad5f05387
diff --git a/setup.cfg b/setup.cfg
index 672e5b0..ff12b10 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -16,7 +16,7 @@
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
+    Programming Language :: Python :: 3.6
 
 [files]
 packages =