fix lexical error
fix lexical error

Summary:
var a = /<!--/;

would not parse correctly. The lexer thought "<!--" was starting a comment and due to the way my lexer is written (as a consequence of /regex/ craziness) the comment trumped the regex.

Reviewed By: epriestley

Test Plan: fbjs2 test suite doesn't have any errors

Revert Plan: ok

facebookarchive/libfbjs,facebookarchive/libfbjs