Pretty-printing precedence issue

Type `(Int => Any) => List[Any]` is shown without the parens:
```scala
scala> :type List(1, 2).map[T = Int]
Int => Any => List[Any]
```
while parens are omitted correctly here:
```scala
scala> val x: Int => (Int => Int) = _ => _ => 1
val x: Int => Int => Int = Lambda$1619/864078397@23310248
```

that is, the pretty-printer misses associativity of `=>`.