Fix BulkDeleteWithConfirmButton does not work when mutationMode is undoable

[fzaninotto]

Problem

When using a BulkActions component with a bulk delete that is both with confirm and undoable, the delete never occurs

const PostListBulkActions = props => (
    <BulkDeleteWithConfirmButton {...props} mutationMode="undoable" />
);

Solution

In undoable mode, it's the the notification's role to trigger the mutation. If the notification doesn't know it's undoable, the mutation never occurs.