Cut a new release for GHC 8.6

[ocharles]

master builds on GHC 8.6 now (well, stm-2.5) - but I don't have release rights. Could you cut a new release?

[ocharles]

Oh, I don't even have commit rights on this repo. Perhaps I could be added? Or would you prefer a PR?

[patrickt]

Would love to see this package work with newer GHCs 👍

[ocharles]

@ivan-m bump.