Fixes the PREG_REPLACE_EVAL usage vulnerability

Usage of e in preg_replace is deprecated due to security vulnerabilities, in place of that preg_replace_callback can be used
http://www.php.net/manual/en/reference.pcre.pattern.modifiers.php
Merge pull request #47 from UmeshSingla/patch-1

 Fixes the PREG_REPLACE_EVAL usage vulnerability