newtypes are formatted on two lines with break_single_constructors: false

As `newtype`s always have a single constructor, you would think that they
would obey `break_single_constructors`. However, with that set to false,
```haskell
newtype Foo = Foo Int
```
becomes
```haskell
newtype Foo
   = Foo Int
```

while `data` with a single constructor stay on one line.
```haskell
data Foo = Foo Int
```
