message: docs: add python version to contributing
  Change-Type: patch
  Changelog-Entry: Add the Python version (2.7) to the CONTRIBUTING doc.
diff: @@ -18,7 +18,7 @@ Developing
  #### Common
  - [NodeJS](https://nodejs.org) (at least v6)
  -- [Python](https://www.python.org)
  +- [Python 2.7](https://www.python.org)
  - [jq](https://stedolan.github.io/jq/)
  - [curl](https://curl.haxx.se/)
  