Setting opts.window should also update isLocation global variable

[joshgillies]

I'm currently playing around with page.js in a Worker context, and as a result of that environment having no native window object, etc I'm passing my own via page.setup({ window: {...} }) - however when it comes to initiating a route we get errors because isLocation is not set.

Would it be possible to update the isLocation variable based on the input object from opts.window?

[matthewp]

Yup! PR welcome here.