fix merge 2.3 into 2.7 for SecureRandom dependency

Author: Tobion

composer.json

@@ -26,7 +26,7 @@
         "symfony/http-kernel": "~2.7",
         "symfony/filesystem": "~2.3",
         "symfony/routing": "~2.6,>2.6.4",
-        "symfony/security-core": "~2.6",
+        "symfony/security-core": "~2.6.13|~2.7.9|~2.8",
         "symfony/security-csrf": "~2.6",
         "symfony/stopwatch": "~2.3",
         "symfony/templating": "~2.1",