revert 1.0 bump and tag + release 0.21.1 instead

[KristofferC]

This allows us to get a new JSON version out to everyone with the latest bugfixes and improvements.

[KristofferC]

Unless someone objects I will merge and tag a new version in not too long.

[TotalVerb]

This will just move the maintenance burden to the 1.0 "branch" instead of the 0.21 "branch". I think this LGTM to get the fix out, but unfortunately we'll need to continue tagging each fix with both version numbers, it seems.

[KristofferC]

There is no 1.0 branch though, since 1.0 was never released.

Edit: Or it was, it was just not tagged here?

Edit: Edit: No it wasn't after all... https://github.com/JuliaRegistries/General/blob/master/J/JSON/Versions.toml

[TotalVerb]

Ah ok, then LGTM. Let's hold off on the 1.0 tag then. (I think that is still a good idea in principle, but will require some script to mass-PR repositories with an upgrade to their Compat.jl entries, plus a potential PR to the General repository. If someone wishes to volunteer this, it could be useful for many package migrations, but until then the change is too disruptive.)