chore: allow node newer than 18

Close #1402

Author: posva

package.json

@@ -4,7 +4,7 @@
   "description": "Official Firebase bindings for Vue.js",
   "packageManager": "[email protected]",
   "engines": {
-    "node": "18"
+    "node": ">=18"
   },
   "volta": {
     "node": "18.16.1"

playground/functions/package.json

@@ -11,7 +11,7 @@
     "logs": "firebase functions:log"
   },
   "engines": {
-    "node": "18"
+    "node": ">=18"
   },
   "main": "lib/index.js",
   "dependencies": {