FIX: reset gravatar cache by adding random param to URL (PR #9370)

Users noticed that sometimes, avatar from Gravatar is not correctly updated - Updated image on gravatar, not seeing it update on site - support - Discourse Meta

A potential reason for that is that even if you update your avatar in Gravatar, URL stays the same and if the cache is involved, service is still receiving the old photo.

For example. In my case, when I click the button to refresh avatar the new Upload record is created with origin URL to new avatar, and url to old one

I made some tests in the rails console and adding random param to Gravatar URL is deceiving cache and correct, the newest avatar is downloaded

GitHub

Seems good to me!

nice! easy-ish fix thank you @lis2! :bowing_man:‍♂