Switch to the new Neovim health API

[DestyNova]

The old report_(start|ok|info|warn|error) functions are deprecated and break :checkhealth in recent versions of neovim:

Error executing lua: function health#lsp#check, line 1: Vim(call):E117: Unknown function: health#report_start
stack traceback:                                                                                                                                                                             
        [C]: in function 'call'                                                                                                                                                              
        /usr/share/nvim/runtime/lua/vim/health.lua:366: in function '_check'                                                                                                                 
        [string "<nvim>"]:1: in main chunk                        

This PR updates to the new vim.health API and fixes the issue, although I guess it will break checkhealth for very old versions.

[prabirshrestha]

Merged. Thanks!

[prabirshrestha]

Well this doesn't work as it seems to break vim. #1562 works for both vim and nevoid.

[prabirshrestha]

This is now fixed in both vim and neovim.

[DestyNova]

Ah, bummer 😮