fix(nvim-lsp): updated highlight group names

[pyrho]

👋

diagnostic-nvim got more or less merged with neovim master; and with that the highlight group names have been changed for consistency with the rest of the LSP related stuff.

I chose to leave the previous groups in there so that it won't mess up the install for people not running bleeding edge neovim:master.

See nvim-lua/diagnostic-nvim#73 for more info.

[skbolton]

Thanks for staying on top of this. I am guessing when neovim hits version 5 as an official release we can delete the old legacy rules?

[pyrho]

I am guessing when neovim hits version 5 as an official release we can delete the old legacy rules?

Indeed, but there is a high chance that I'll forget to do that when nvim 5 will be out (:

[skbolton]

I'll watch it as well and make the change when time comes. Thanks again.