Update composer.json

The firebase/php-jwt package contains a vulnerability that can only be
resolved by going to 7.x. I didn't want to also change the requirements
of this package as part of the redirect fix.

Author: markstory

composer.json

@@ -80,6 +80,11 @@
         "sort-packages": true,
         "allow-plugins": {
             "dealerdirect/phpcodesniffer-composer-installer": true
+        },
+        "policy": {
+            "advisories": {
+                "ignore": ["PKSA-y2cr-5h3j-g3ys"]
+            }
         }
     },
     "minimum-stability": "dev",