Require PHP >= 5.4

We need PHP 5.4 or later so $this references inside closures work, which we require for checks as they use $this->add_error().

.travis.yml

@@ -1,7 +1,7 @@
 language: php
 
 php:
-    - 5.3
+    - 5.4
     - 5.5
 
 env:

readme.md

@@ -4,7 +4,7 @@ A WordPress plugin that enables you to scan all sorts of themes and files and th
 
 Contributors: [Mohammad Jangda](http://profiles.wordpress.org/batmoo/), [Automattic](http://profiles.wordpress.org/automattic/), [Thorsten Ott](http://profiles.wordpress.org/tott/), [Michael Fields](http://profiles.wordpress.org/mfields/), [Filipe Varela](http://profiles.wordpress.org/keoshi/), [Josh Betz](http://profiles.wordpress.org/betzster/), [Mike Blouin](https://github.com/Mobius5150), [Nick Daugherty](http://profiles.wordpress.org/nickdaugherty/) and [Fränk Klein](https://profiles.wordpress.org/frank-klein/).
 
-Requires WordPress version 3.4 or greater.
+Requires WordPress version 3.4 or greater and PHP >= 5.4.
 
 
 About

readme.txt

@@ -17,6 +17,8 @@ This plugin is based on code from the <a href="http://wordpress.org/extend/plugi
 
 == Requirements ==
 
+VIP Scanner requires PHP >= 5.4.
+
 For parsing PHP files, VIP Scanner uses [PHP-Parser](https://github.com/nikic/PHP-Parser),
 which it includes as a git submodule. When cloning VIP Scanner's git repo, use
 the `--recursive` parameter to include PHP-Parser, i.e.