Support OCaml 4.14

[novaluke]

• Update ppxlib to ^0.26.0 to gain OCaml 4.14 support
• Update ocaml to 4.14.x to fix Migration error: existentials in pattern-matching is not supported before OCaml 4.13 when running the PPX on files with existentials in pattern matching

[anmonteiro]

Thank you! @ryb73 could we get a new release with this fix?

[ryb73]

Hey @mayhewluke, @anmonteiro, thanks for the PR. Unfortunately because Travis doesn't offer a free tier anymore, my CI/CD pipeline is broken and I can no longer build and publish cross-platform binaries. I don't know the best way to proceed, but it seems like it might be best to transition away from publishing pre-built binaries and instead use an npm postinstall hook to build on the client side? @anmonteiro you seem to have more Reason + PPX experience, what do you think?

[novaluke]

@ryb73 I'm no expert here, so I'll defer to @anmonteiro, but building on the client side would be handy for me. I'm on NixOS, and pre-built binaries don't work for it (unless built with Nix itself), so I have to remember to patch the binary after each npm re-install. Building on the client-side would give a seamless experience on NixOS, but that's only a small subset of the user base, so that may not be a significant consideration here.

[rolandpeelen]

@ryb73 - My Lens PPX is heavily inspired by your workflow - I build it using Github Actions, by tagging releases it pushes to NPM.

Perhaps we can use something like that here as well?

https://github.com/rolandpeelen/bs-pancake/tree/master/.github/workflows

The only thing lacking there is Windows support - I don't have access a windows machine here / don't really develop on one so I have no idea on how to deal with it :)

[rolandpeelen]

This should fix it: #85 :)

[ryb73]

This PR has been released in v1.6.0. Thanks again @mayhewluke and @rolandpeelen!