`:=` and `:=!` too losely bound

I'm not sure it's even possible to fix this but you'll notice that when defining a record with function types, you must use parenthesis like this:

```haskell
type MyRec = R ( "runThing" := (a -> IO b) )
```

Without parens, the parser thinks you are defining `("runThing" := a) -> IO b` as an unlabeled record.