Update rust version to 1.22.1

[Majora320]

Fixes#556

[kazk]

Thanks for contributing.

Is 1.22.1 100% compatible (without any deprecation) with 1.15.1? If not, we can't accept this PR because we need to keep the existing contents working.

Currently, most languages can have only one version and maintaining backward compatibility has been really painful. So we've been working on a new project to replace this one. Sorry for not making this clear.

[Majora320]

@kazk
Looking through the release notes here, it looks like there were no breaking changes since 1.15.1. TcpListener::set_only_v6was deprecated in 1.16.0, but using it only emits a warning, and it's unlikely to have been used at all.

Edit: Never mind.
https://github.com/rust-lang/rust/blob/master/RELEASES.md#compatibility-notes,
https://github.com/rust-lang/rust/blob/master/RELEASES.md#compatibility-notes-2,
https://github.com/rust-lang/rust/blob/master/RELEASES.md#compatibility-notes-3,
https://github.com/rust-lang/rust/blob/master/RELEASES.md#compatibility-notes-4,
https://github.com/rust-lang/rust/blob/master/RELEASES.md#compatibility-notes-5,
https://github.com/rust-lang/rust/blob/master/RELEASES.md#compatibility-notes-6

[Majora320]

I suppose this isn't useful then, should I close it?

[kazk]

@Majora320
Yeah, I'll have to close this. Sorry for not making the compatibility requirement clear.

I just want to let you know that supporting newer language versions is definitely on our roadmap. The new project allows us to add new language version support quickly without worrying about existing contents. I can't say when it'll be available yet because we're also reworking the infrastructure and that's taking longer than expected.