Use GhcModT everywhere and remove the GhcMod alias

Not doing this makes having GhcModT pretty pointless as users of the
library wouldn't be able to use custom inner monads as evey function for
dealing with GhcModT's would be constraint to (GhcModT IO) thus only
allowing IO as the inner monad.

Language/Haskell/GhcMod/Lint.hs

@@ -11,8 +11,9 @@ import Language.Haskell.HLint (hlint)
 
 -- | Checking syntax of a target file using hlint.
 --   Warnings and errors are returned.
-lint :: FilePath  -- ^ A target file.
-     -> GhcMod String
+lint :: IOish m
+     => FilePath  -- ^ A target file.
+     -> GhcModT m String
 lint file = do
   opt <- options
   ghandle handler . pack =<< (liftIO $ hlint $ file : "--quiet" : hlintOpts opt)