Documentation: fix and clarify opam 2.1 switch creation

[vphantom]

Issue Description

The opam 2.1 switch creation examples in the release notes for OCaml 4.12.1+ included an incorrect extra - and did not match the <2.1 example with two options.

Changes Made

In the three release notes' opam 2.1 example, I removed the extra - and added the missing nnpchecker option to match the other example and show how multiple options are now separated by spaces instead of commas.

• Please check if the PR fulfills these requirements

• [x] ❗ If the PR changes a markdown document in site/, a comment was added in https://github.com/ocaml/ood/issues/52 with a link to the PR

• [x] PR is descriptively titled and links the original issue above

• [ ] Before/after screenshots (if this is a layout change)

• [ ] Details of which platforms the change was tested on (if this is a browser-specific change)

• [ ] Context for what motivated the change (if this is a change to some content)

[patricoferris]

Thanks, the CI errors are unrelated I think. I think opam.ocaml.org went through some maintenance and https://opam.ocaml.org/json/last10_updates.json was probably down. Merging now (thanks for the v3 pointer too)

[vphantom]

Thanks, the CI errors are unrelated I think.

I think the problem is that I edited my message twice very shortly after submitting it and it seems to have triggered three checks in quick succession. Had I known that editing the message caused this, I would've proof-read a few more times before my initial submission. 😉

[patricoferris]

Ah no, I think it is because opam.ocaml.org is now fully https so the curl returns nothing:

• curl http://opam.ocaml.org/json/last10_updates.json is empty
• curl https://opam.ocaml.org/json/last10_updates.json works

See https://deploy.ci3.ocamllabs.io/job/2021-10-27/134900-ocluster-build-14a940

[patricoferris]

Your changes are live @vphantom, thanks again :)) https://ocaml.org/releases/4.13.1.html