Adds depreciation notes for Parse.Cloud.useMasterKey(), (#3204)

Adds depreciation notes for Parse.Cloud.useMasterKey()

src/cloud-code/Parse.Cloud.js

@@ -59,6 +59,11 @@ ParseCloud._removeAllHooks = () => {
   triggers._unregisterAll();
 }
 
+ParseCloud.useMasterKey = () => {
+  // eslint-disable-next-line
+  console.warn("Parse.Cloud.useMasterKey is deprecated (and has no effect anymore) on parse-server, please refer to the cloud code migration notes: https://github.com/ParsePlatform/parse-server/wiki/Compatibility-with-Hosted-Parse#cloud-code")
+}
+
 ParseCloud.httpRequest = require("./httpRequest");
 
 module.exports = ParseCloud;