Simplify sort URL path
Simplify sort URL path

Use the current resource's `sort` action, which handles nested and
non-nested resources.

hotvulcan/activeadmin-sortable-tree,zorab47/active_admin-sortable_tree,tripledub/activeadmin-sortable-tree,NHSChoices/activeadmin-sortable-tree,hotvulcan/activeadmin-sortable-tree,hotvulcan/activeadmin-sortable-tree,zorab47/activeadmin-sortable-tree,wvengen/activeadmin-sortable-tree,zorab47/active_admin-sortable_tree,zorab47/activeadmin-sortable-tree,zorab47/activeadmin-sortable-tree,zorab47/active_admin-sortable_tree