Update the PHP requirement information

Author: bsweeney

README.md

@@ -48,7 +48,7 @@ Follow us on [![Twitter](http://twitter-badges.s3.amazonaws.com/twitter-a.png)](
 
 ## Requirements
 
- * PHP version 5.3.0 or higher
+ * PHP version 5.4.0 or higher
  * DOM extension
  * GD extension
  * MBString extension