Py Docs: Fix json URL

In the future when we have a docs staging area it will be
important to change where this JSON is pulled from.
For now, always pull from the "Production" versions

doc/python_api/static/js/version_switch.js

@@ -1,7 +1,7 @@
 (function() {  // switch: v1.2
 "use strict";
 
-var versionsFileUrl = "https://docs.blender.org/versions.json"
+var versionsFileUrl = "https://docs.blender.org/PROD/versions.json"
 
 var all_versions;