[DOCS] https://firebase.google.com/docs/firestore/solutions/presence#updating_globally not correct example

[albor09]

https://firebase.google.com/docs/firestore/solutions/presence#updating_globally

Updating Cloud Firestore globally example is not correct and same as another example below

[charlesfries]

This is the code that should be displayed there: https://github.com/firebase/functions-samples/blob/main/Node-1st-gen/presence-firestore/functions/index.js