Bump php to 5.6

Author: cursedcoder

composer.json

@@ -12,7 +12,7 @@
   ],
   "homepage": "https://github.com/cursedcoder/eprocess",
   "require": {
-    "php": ">=5.5",
+    "php": ">=5.6",
     "react/react": "~0.4@dev",
     "jms/serializer": "^1.1",
     "doctrine/collections": "~1.3",