updog: upgrade signal-hook

[webern]

Signal hook is at signal-hook = "0.1.13", but the current version is 0.3. When I tried the upgrade some breaking change occurred which I think is out-of-scope for the more mechanical version bumps that I am currently applying.

Specifically:

error[E0599]: no method named `cloned` found for struct `signal_hook::iterator::SignalsInfo` in the current scope
   --> updater/updog/src/main.rs:449:30
    |
449 |     let signals_bg = signals.cloned();
    |                              ^^^^^^ method not found in `signal_hook::iterator::SignalsInfo`

This should probably be tackled in isolation to ensure nothing about the API breaks.