Added script to update integration test version

Author: Nyholm

composer.json

@@ -31,7 +31,8 @@
         "league/flysystem":     "^1.0"
     },
     "require-dev":       {
-        "phpunit/phpunit":         "^4.0|^5.1"
+        "phpunit/phpunit":         "^4.0|^5.1",
+        "cache/integration-test": "0.7.0"
     },
     "provide":           {
         "psr/cache-implementation": "^1.0"