Requires the virtual implementation

Author: Nyholm

composer.json

@@ -25,7 +25,7 @@
         "symfony/framework-bundle":      "^2.7|^3.0",
         "doctrine/cache":                "^1.3",
         "aequasi/psr-6-doctrine-bridge": "^1.2",
-        "psr/cache":                     "dev-master"
+        "psr/cache-implementation":      "~1.0"
     },
     "require-dev":  {
         "phpunit/phpunit": "^5.1|^4.0"