Add 'request' param to set_cookie examples

[michaeljones]

It seems to be necessary and it seems like the docs aren't in sync but I might be wrong.

[lpil]

Hello! If you look closely you'll see that the request parameter is being piped in, so with this patch you'd be supplying the request as the first and the second argument, which is not valid.

[michaeljones]

I think the repsonse parameter is being piped in but set_cookie wants both the response and the request as the first two arguments?

[lpil]

Sorry, you're right! I read this too fast.

Thanks!