Try to fix markdown indentation after reading issues

See https://github.com/remarkjs/remark-lint/issues/178

CONTRIBUTING.md

@@ -2,14 +2,14 @@
 
 Contributions are welcome, as long as they respect our current workflow:
 
- 1. The master branch is only for releases. Once properly tested,
+1.  The master branch is only for releases. Once properly tested,
  the dev branch can be merged, the release tagged and a tar archive
  created.
 
- 2. The dev branch should never be commited to directly, unless
+2.  The dev branch should never be commited to directly, unless
  you're updating the CHANGELOG file.
 
- 3. Use feature branches for anything else, once they've passed all
+3.   Use feature branches for anything else, once they've passed all
  CI test, lints and have been reviewed by other contributors through a
  pull request, they may be merged into the dev branch.