Wrong type definition in api-type.html#response-headers

In https://haskell-servant.github.io/tutorial/api-type.html#response-headers, the line

```
type UserAPI = "users" :> Get '[JSON] (Headers [Header "User-Count" Integer] [User])
```

should read

```
type UserAPI = "users" :> Get '[JSON] (Headers '[Header "User-Count" Integer] [User])
```

otherwise the example won't compile.
