Don't break previous configs without xvfb
Move the check for how many requests are left inside the last_request_timeout function

Without this change `current_requests` could be zero, triggering the
last_request_timeout and then a new request could come in, and wouldn't
be caught.
Move render logic into separate function

I think we should edit the readme to show how devs can create a new
snap.js file without affecting the repo, enabling them to gets updates
to the project a lot easier