Update slog-syslog depdencies

[omarabid]

The syslog dependency is outdated and there is a new version.

[stouset]

Seconded 👍

[dpc]

Is there a PR? :D

[stouset]

I took a first swag at it but being unfamiliar with both codebases I ran into some hurdles. I'll keep poking at it but I suspect you'd be able to do this in about a tenth of the time.

[cezarmathe]

Hello! Is anyone working on this? If not, I would like to look into it myself.

Out of topic: I've just opened a PR for other improvements for the syslog drain: slog-rs/syslog#7.

[stouset]

I took a look a few months back but I wasn't familiar enough with the code base to make much headway.