Merge pull request #810 from octodns/py3-contributing

Fix python version support in CONTRIBUTING.md

CONTRIBUTING.md

@@ -35,7 +35,7 @@ Here are a few things you can do that will increase the likelihood of your pull
 
 - Keep your change as focused as possible. If there are multiple changes you would like to make that are not dependent upon each other, consider submitting them as separate pull requests.
 
-- We target Python 2.7, but have taken steps to make Python 3 support as easy as possible when someone decides it's needed. PR welcome.
+- We target Python 3, support for Python 2 has been dropped.
 
 - Write a [good commit message](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html).