Revised Monad[Task].point to evaluate lazily

@pchiusano said he had a reason for `Monad[Task].point` evaluating eagerly, but he couldn't remember what it was.  Submitting PR for further review.

For the purposes of discussion, bear in mind that `Monad[IO].point` is lazy.
@djspiewak In case this is going to happen, could you please make the equivalent change for `Future` too?