Wrap attribute selector query in quotes
Wrap attribute selector query in quotes

As of jQuery 1.12 the selector `a[href$=abc]` is invalid and requires
quotes around the value part.

Fixes failing test

See:
https://github.com/jquery/jquery/issues/2824
https://github.com/alphagov/static/pull/874

alphagov/static,alphagov/static,alphagov/static