Declare compatibility with python 3.5

To be able to run the tests with py3, we need to declare the right
classifier.

Change-Id: I6ba0cda5af99721fbd3fe28a1bf107a38c08b195
diff --git a/setup.cfg b/setup.cfg
index 6960fa2..6054053 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -16,6 +16,8 @@
     Programming Language :: Python
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
+    Programming Language :: Python :: 3
+    Programming Language :: Python :: 3.5
     Topic :: Internet :: Name Service (DNS)
 
 [global]