Build with GHC 8.8

[pkamenarsky]

This removes the tls upper bound, since versions of tls < 1.5 (e.g. 1.4.1, and maybe later versions too?) don't build with GHC 8.8 due to a missing MonadFail constraint.

tls                              > /tmp/stack-5280da6a145234f9/tls-1.4.1/Network/TLS/Packet.hs:648:27: error:
tls                              >     • Could not deduce (MonadFail m) arising from a use of ‘fail’
tls                              >       from the context: Monad m
tls                              >         bound by the type signature for:
tls                              >                    fromJustM :: forall (m :: * -> *) a.
tls                              >                                 Monad m =>
tls                              >                                 String -> Maybe a -> m a
tls                              >         at Network/TLS/Packet.hs:647:1-48
tls                              >       Possible fix:
tls                              >         add (MonadFail m) to the context of
tls                              >           the type signature for:
tls                              >             fromJustM :: forall (m :: * -> *) a.
tls                              >                          Monad m =>
tls                              >                          String -> Maybe a -> m a
tls                              >     • In the expression: fail ("fromJust " ++ what ++ ": Nothing")
tls                              >       In an equation for ‘fromJustM’:
tls                              >           fromJustM what Nothing = fail ("fromJust " ++ what ++ ": Nothing")
tls                              >     |
tls                              > 648 | fromJustM what Nothing  = fail ("fromJust " ++ what ++ ": Nothing")
tls                              >     |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
tls                              >