Fixed requirements of doctrine/persistence (#193)

Author: lyrixx

composer.json

@@ -15,6 +15,7 @@
         "php": "^7.1.3",
         "doctrine/collections": "^1.5",
         "doctrine/common": "^2.11|^3.0",
+        "doctrine/persistence": "^1.3|^2",
         "doctrine/doctrine-bundle": "^1.8|^2.0",
         "doctrine/orm": "^2.6",
         "easycorp/easyadmin-bundle": "^2.2.2",