Remove Lexer#color monkey patch

The new Sass parser source maps give us enough information to no longer
require this patch.

Change-Id: I57e1ba0c83773036ec476643d2f5c543f2ac0a07
Reviewed-on: http://gerrit.causes.com/36427
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>