New features must always target the master branch (#1334)

CONTRIBUTING.md

@@ -10,8 +10,8 @@ There are a few basic ground-rules for contributors:
 
 1. **No `--force` pushes** on `master` or modifying the Git history in any way after a PR has been merged.
 1. **Non-master branches** ought to be used for ongoing work.
-1. **External API changes and significant modifications** ought to be subject to an **internal pull-request** to solicit feedback from other contributors.
-1. Internal pull-requests to solicit feedback are *encouraged* for any other non-trivial contribution but left to the discretion of the contributor.
+1. **Non-trivial changes** ought to be subject to an **internal pull-request** to solicit feedback from other contributors.
+1. All pull-requests for new features **must** target the `master` branch. PRs to fix bugs in LTS releases are also allowed.
 1. Contributors should attempt to adhere to the prevailing code-style.
 1. 100% code coverage