Use notice flash type rather than nonexistent info.

app/controllers/groups/group_members_controller.rb

@@ -63,7 +63,7 @@ class Groups::GroupMembersController < Groups::ApplicationController
     
     if can?(current_user, :destroy_group_member, @group_member)
       @group_member.destroy
-      redirect_to(dashboard_groups_path, info: "You left #{group.name} group.")
+      redirect_to(dashboard_groups_path, notice: "You left #{group.name} group.")
     else
       return render_403
     end