loosen typing of two event listener functions

The functions in question apply to events emitted by both Readable and
Writable streams. They were typed so as to only apply to Readable
streams.

Author: matthewleon

src/Node/Stream.purs

@@ -207,14 +207,14 @@ foreign import onFinish
 -- | Listen for `close` events.
 foreign import onClose
   :: forall w eff
-   . Readable w eff
+   . Stream w eff
   -> Eff eff Unit
   -> Eff eff Unit
 
 -- | Listen for `error` events.
 foreign import onError
   :: forall w eff
-   . Readable w eff
+   . Stream w eff
   -> (Error -> Eff eff Unit)
   -> Eff eff Unit