Update 'Edit this page' link regex

[22a]

This PR updates the Edit this page link filter regex from

• template.+(hbs|md)
  to
• \.(hbs|md)$

this removes the necessity to have the string "template" in doc filenames, in turn preventing dead links such as https://github.com/user/repo/edit/branch/undefined

I'm not too concerned about the trailing $ if it's not agreeable but happy to discuss.

[dfreeman]

Thanks @22a! This seems reasonable to me, but @samselikoff should probably confirm. I wonder if there's a lightweight way to include test coverage for this so we don't regress in the future?

[samselikoff]

Even a hard-coded test for a currently existing docs page would be great

[22a]

@dfreeman @samselikoff Good point, added!

[samselikoff]

Thank you!