End the update request once the end time is reached

This avoids the infinite refreshes that the code used to cause prior to
this change.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Don't hardcode host, port, etc

This actually will still work even if the website switches to https or
starts to require authentication (neither of which is currently supported
on the server side / visualize.js).

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>