Fix MonadFail import

[jezen]

I believe since GHC 8.0.1 we need to import fail and MonadFail from Control.Monad.Fail instead of Control.Monad. I also believe that this is a temporary measure, and this changes again from GHC 8.8.1.

More:

• https://downloads.haskell.org/~ghc/8.0.2/docs/html/users_guide/glasgow_exts.html#ghc-flag--XMonadFailDesugaring
• https://wiki.haskell.org/MonadFail_Proposal