.travis.yml: Use Python version '3.6'

Python 3.6 has been released, and the old Travis CI '3.6-dev'
environment can be accessed using '3.6'.

Author: jayvdb

.travis.yml

@@ -6,7 +6,7 @@ python:
 - '3.3'
 - '3.4'
 - '3.5'
-- '3.6-dev'
+- '3.6'
 env:
 - TOXENV=py-test
 
@@ -46,4 +46,4 @@ deploy:
   - <<: *pypi
     on:
       tags: true
-    distributions: "bdist_egg"
+    distributions: "bdist_egg"