allow old firebase-functions versions

Author: Berlioz

package.json

@@ -48,7 +48,7 @@
     "@types/mocha": "^5.2.7",
     "chai": "^4.2.0",
     "firebase-admin": "^12.0.0",
-    "firebase-functions": "^6.0.1",
+    "firebase-functions": "^4.9.0",
     "firebase-tools": "^8.9.2",
     "mocha": "^6.2.2",
     "prettier": "^1.19.1",
@@ -58,7 +58,7 @@
   },
   "peerDependencies": {
     "firebase-admin": "^8.0.0 || ^9.0.0 || ^10.0.0 || ^11.0.0 || ^12.0.0",
-    "firebase-functions": ">=6.0.1",
+    "firebase-functions": ">=4.9.0",
     "jest": ">=28.0.0"
   },
   "engines": {