RegexUtil.js: Fix for CMv4 (Brackets Sprint 38+)

Guess you just missed this file

https://github.com/adobe/brackets/wiki/Brackets-CodeMirror-v4-Migration-Guide

> CodeMirror is no longer global. In Brackets, we used to provide CodeMirror as a global. CodeMirror now supports require(), so we now include CodeMirror as a module instead. This means you should add var CodeMirror = brackets.getModule("thirdparty/CodeMirror2/lib/codemirror"); at the top of any module that accesses the CodeMirror object. Sprint 38 will still provide the global CodeMirror (which is the same as the module-loaded CodeMirror), but access to it is deprecated and it will be removed in a future release. (Note that this doesn't affect accesses to editor._codeMirror, which should work as before.)