Fix: Task delete has incorrect output message

[vprusso]

In taskController.js the delete function has an incorrect message:

exports.delete = async function (req, res) {
  routeWrapper(res,
    async () => await taskService.delete(req.params.id),
    'New task added to submission!')
}

The message should be Successfully deleted task or something to that effect.

[vprusso]

Closing from #96