📙 Fix json example

[MrMartinR]

Link to section:
https://docs.parseplatform.org/rest/guide/#hooks

What is the issue?
The json example is malformed

Can you propose a solution?
change {"functionName" : x, "url" : y} to {"functionName": "foo", "url": "https://api.example.com/foo"}

[mtrezza]

Closing via #885