Add support for @ and _ as prefix to locals variable

With the commit: https://github.com/rtomayko/tilt/commit/d4c67207dbc02aced72b13ddd1b1f0e8b08b2526 and the consequent version bump, we issues a problem with our code because we are using as locals the @ before a variable name and sometimes also the underscore. While until 1.3.3 it was working flawlessly now we hit the wall.

The issue is actually fixable just slightly modifying the regex with: \A(@|_)?[a-z]\w*\z 

This patch fix the issue