Updates PHP version requirements to match those of Laravel 5.4

Author: Harrisonbro

composer.json

@@ -10,7 +10,7 @@
     ],
     "license": "MIT",
     "require": {
-        "php" : "^5.5|^7.0",
+        "php" : "^5.6|^7.0",
         "illuminate/support": "^5.4",
         "illuminate/session": "^5.4"
     },