Audit: Regexp.escape formula names

We allow certain special regex characters in formula names, and if
those aren't escaped when interpolating them into a regex, they'll be
interpreted as special regex characters.

This can cause regex compile errors on Ruby 1.8 (for example, with
"libxml++3", which has nested match characters), and more subtle
matching bugs in general.

Refs an issue surfaced in Homebrew/homebrew#48744.

Closes Homebrew/homebrew#49005.

Signed-off-by: Misty De Meo <mistydemeo@gmail.com>