Add MockCloudEvents for RTDB-V2 (#156)

* Add and handle MockCloudEvents for RTDB-V2

This commit is a follow-up to firebase-function's addition of rtdb-v2, firebase/firebase-functions#1127.

Wrap can now handle:

* `database.onValueCreated`
* `database.onValueDeleted`
* `database.onValueUpdated`
* `database.onValueWritten`

package.json

@@ -47,7 +47,7 @@
     "@types/mocha": "^5.2.7",
     "chai": "^4.2.0",
     "firebase-admin": "^10.1.0",
-    "firebase-functions": "^3.21.0",
+    "firebase-functions": "^3.22.0",
     "firebase-tools": "^8.9.2",
     "mocha": "^6.2.2",
     "prettier": "^1.19.1",
@@ -57,7 +57,7 @@
   },
   "peerDependencies": {
     "firebase-admin": ">=6.0.0",
-    "firebase-functions": ">=3.21.0",
+    "firebase-functions": ">=3.22.0",
     "jest": ">=28.0.0"
   },
   "engines": {