Fix: register an offence when the last hash parameter has braces.

The following code will now register an offence, see discussion in https://github.com/bbatsov/rubocop/pull/551/files#r6921166.

``` ruby
where(1, { y: 2 })
```

However, when you have multiple hash parameters, it will not to avoid the ugly

``` ruby
where({ x: 1 }, y: 2)
```