Use text.html.erb scope for HTML+ERB files

This grammar does a better job highlighting than the text.html.ruby grammar does. It requires injection grammar support, but there's no getting around that.
Merge pull request #1641 from github/aroben-patch-1

Use text.html.erb scope for HTML+ERB files
Bumping version for 3.4.1 release
Merge pull request #1643 from github/linguist-3.4.1

Bumping version for 3.4.1 release