Update to regex-single-quoted to place the constant.character.escape.php inside the patterns array so as to fix the broken regex highlighting in single quoted php regular expressions.

Cleanup code for PR atom#134 that fixes single quoted regex in php.

adding spec for escaped bracket and trying to get working. Currently
the tokenizer does not parse the test case correctly. Trying to
determine issue

spec to check if the single quoted PHP string parses escaped characters
correctly is now working correctly. It fails when the fix for atom#124 is
removed, but passes when the fix is in place, just as desired.