Update dependency firebase-functions to v3 (#1967)

Author: renovate-bot

config/functions/package.json

@@ -4,7 +4,7 @@
   "dependencies": {
     "cors": "2.8.5",
     "firebase-admin": "8.2.0",
-    "firebase-functions": "2.3.1"
+    "firebase-functions": "3.1.0"
   },
   "private": true
 }

packages/auth/demo/functions/package.json

@@ -10,7 +10,7 @@
   },
   "dependencies": {
     "firebase-admin": "8.2.0",
-    "firebase-functions": "2.3.1"
+    "firebase-functions": "3.1.0"
   },
   "private": true
 }