Friendica PHP requirement bumped to version 7.2+

Hi !Friendica Admins,

The upcoming version 2021.09 of Friendica won't entirely work on systems with a PHP version under 7.2. The specific feature are the push notifications as part of the Mastodon API, but it is highly recommended to upgrade your PHP installation if it wasn't already.

For administrators running the develop branch, the version bump is effective immediately.