Fix type of exists

Author: paf31

src/Node/FS/Async.purs

@@ -329,7 +329,7 @@ appendTextFile encoding file buff cb = mkEff $ \_ -> runFn4
 -- Check if the path exists.
 --
 exists :: forall eff. FilePath
-                   -> (Boolean -> Eff eff Unit)
+                   -> (Boolean -> Eff (fs :: FS | eff) Unit)
                    -> Eff (fs :: FS | eff) Unit
 exists file cb = mkEff $ \_ -> runFn2
   fs.exists file $ \b -> runPure (unsafeInterleaveEff (cb b))