Changed require-dev phpunit version limits to include ^4.0

composer.json

@@ -17,11 +17,11 @@
         }
     ],
     "require": {
-        "php" : ">=5.5.0",
+        "php" : ">=5.6.0",
         "illuminate/support": "~5.2"
     },
     "require-dev": {
-        "phpunit/phpunit" : "~5.7",
+        "phpunit/phpunit" : "^4.0|^5.0",
         "orchestra/testbench": "~3.0",
         "doctrine/dbal": "~2.3"
     },