Enable the const_unsafe_cell_new feature flag for nightly

[jedisct1]

No description provided.

[KodrAus]

Thanks @jedisct1!

This depends on mvdnes/spin-rs#42

[KodrAus]

This looks good to me. @Kimundi are we ok to merge this and push out a point release?

[KodrAus]

Another fix for this I think would be #55 which removes the need for this feature flag.

[Kimundi]

Looks good, thanks!

[joshlf]

Looks like this might not be sufficient - since the version of spin that's required is just 0.4, existing Cargo.lock files with 0.4.5 or below will still cause breakage because spin only fixed this issue in 0.4.6.

[sfackler]

It seems pretty expected that people may have to update dependencies to fix bugs?

[joshlf]

Well right now, this will just show itself as a compilation failure - it wouldn't be obvious that updating to a newer version would fix things. If we changed the dependency to spin = 0.4.6, then it would show itself as a failure to resolve dependencies, which would make it very obvious what needed to be done.