Reset timeout when each service is up

[jayvdb]

I use wait-for-them to monitor a bunch of Rust services being built & run.
They build sequentially because of cargo wanting a global file lock on the package cache & build directory.

It would be helpful if there was a new mode for wait-for-them which reset the timeout each time one of the services comes online, which indicates that there is progress towards the objective of them all being reachable.