WordPress required version update

Hi !

Please note that BuddyPress 10.0.0 will require WordPress >= 5.4.

To learn more about this change: https://buddypress.trac.wordpress.org/changeset/13140

To learn more about how we decide to bump our WordPress required version: https://codex.buddypress.org/getting-started/wordpress-version-compatibility/

👋

#10-0-0, #wp-requirements