[HTTPS-Everywhere] Maintainability changes to HTTPS Everywhere

[Jacob Hoffman-Andrews]

> I just wanted to point out that contributors can change the target
branch of PR (last I checked) either. They'll have to close their
existing PR and open a new one. If you want that branch to be targetted
by default, you should make it the default branch through the GitHub UI.
I can walk you through this over IRC if you're unfamiliar with it.

Excellent point, thanks. I've been able to change the target branch of a
pull request on my own PRs in the past, but now I realize that's only
*before* they've been submitted as a PR.

I've considered making 4.0 the default target for pull requests, but I
think the majority of our pull requests are actually new rulesets, and
so it's appropriate that they go against master.