Remove support for PHP 5.4

.travis.yml

 language: php
 
 php:
-  - 5.4
   - 5.5
   - 5.6
 

composer.json

@@ -10,7 +10,7 @@
     ],
     "license" : "MIT",
     "require": {
-        "php": ">=5.4.0",
+        "php": ">=5.5.0",
         "ext-mongo": "*",
         "illuminate/support": "5.0.*",
         "illuminate/container": "5.0.*",