Function of a single tuple is ascribed incorrect parentheses

Expected:
```scala
def foo = (x: (String, Int)) => x._2
```

Obtained:
```scala
def foo: (String, Int) => Int = (x: (String, Int)) => x._2
```

Expected:
```scala
def foo: ((String, Int)) => Int = (x: (String, Int)) => x._2
```