consider degrading log version from 0.4 to 0.3

[siddontang]

It shows Unknown for the file name in TiKV log, and hard to debug for us.

[BusyJay]

I don't think it's a bug of this crate. Better let TiKV upgrade its log dependency to 0.4.

[siddontang]

now, it is hard to upgrade to log 0.4 because slog doesn't support it.

@breeswish

[BusyJay]

Then it sounds like a bug of slog.

[siddontang]

yes, but now we have no time to fix it for slog. So the better way is to degrade log version.

[breezewish]

I don't think it's a good idea. Downgrading a dependency to an outdated version is not friendly for the community. Other people who are using this crate will suffer issues. Meanwhile, we are not meeting much trouble when raft.rs using log 0.4.