Remove PHP 5.4 or less support (key() support array is only starting PHP 5.5)

Author: Mathieu Dumoulin

.gitignore

@@ -1,3 +1,4 @@
 .idea
 composer.lock
-vendor
+vendor
+tests/Report

.travis.yml

@@ -1,8 +1,6 @@
 language: php
 
 php:
-  - 5.3
-  - 5.4
   - 5.5
   - 5.6
   - 7

README.md

@@ -28,6 +28,10 @@ To install it, just include this requirement into your composer.json
 ```
 And then run composer install/update as necessary.
 
+# Supports
+
+Only PHP 5.5 or more can be supported due to the fact that key() can only return arrays starting with PHP 5.5!
+
 # Examples
 
 To use the PreviousCurrentIterator, just instanciate a copy with an array and foreach it!