Only distribute from Python 3.6.

Now that PyOTA has universal wheels again, we don't need to build distros using different versions of Python.

Author: todofixthis

.travis.yml

@@ -9,6 +9,7 @@ script: nosetests
 deploy:
   on:
     branch: master
+    python: '3.6'
   provider: pypi
   distribution: 'bdist_wheel sdist'
   skip_upload_docs: true