invalid example code on language spec 3.7 Specifying Types

https://github.com/Microsoft/TypeScript/blob/af4a12151c7f1b0cfe6b913d7c092b825cf4f641/doc/spec.md#3.7

following code is invalid.

``` TypeScript
((x: string) => string) | (x: number) => number)
```

in 3.7

> parentheses are required around function or constructor types in union types.

I think this example should be

``` TypeScript
((x: string) => string) | ((x: number) => number)
```
