Add symfony/security-core to composer.json (#250)

Author: covex-nn

composer.json

@@ -15,7 +15,8 @@
     ],
     "require": {
         "php": "^7.1",
-        "symfony/framework-bundle": "^2.8 || ^3.3 || ^4.0"
+        "symfony/framework-bundle": "^2.8 || ^3.3 || ^4.0",
+        "symfony/security-core": "^2.8 || ^3.3 || ^4.0"
     },
     "require-dev": {
         "symfony/security-bundle": "^2.8 || ^3.3 || ^4.0",