Surround named binding with parens

There is no semantic difference in the code here.
In 0.12.x, it parses fine.
In 0.13.x, it fails to parse.
To make this version of the code work with both versions,
we wrap this named binding with parens.

Author: joneshf

src/Halogen/VDom/DOM.purs

@@ -97,7 +97,7 @@ buildElem = render
     let
       node = DOMElement.toNode el
       onChild = EFn.mkEffectFn2 \ix child → do
-        res@Step n m h ← EFn.runEffectFn1 build child
+        res@(Step n m h) ← EFn.runEffectFn1 build child
         EFn.runEffectFn3 Util.insertChildIx ix n node
         pure res
     steps ← EFn.runEffectFn2 Util.forE ch1 onChild