Update highlights for Neovim LSP diagnostics

After neovim/neovim#12655 has been merged,
highlights have changed a little, so this commit updates the obsolete
highlight groups.

colors/nord.vim

@@ -571,12 +571,16 @@ call s:hi("CocErrorSign" , s:nord11_gui, "", s:nord11_term, "", "", "")
 call s:hi("CocInfoSign" , s:nord8_gui, "", s:nord8_term, "", "", "")
 call s:hi("CocHintSign" , s:nord10_gui, "", s:nord10_term, "", "", "")
 
-" Nvim LSP
-" > neovim/nvim-lsp
-call s:hi("LSPDiagnosticsWarning", s:nord13_gui, "", s:nord13_term, "", "", "")
-call s:hi("LSPDiagnosticsError" , s:nord11_gui, "", s:nord11_term, "", "", "")
-call s:hi("LSPDiagnosticsInformation" , s:nord8_gui, "", s:nord8_term, "", "", "")
-call s:hi("LSPDiagnosticsHint" , s:nord10_gui, "", s:nord10_term, "", "", "")
+" Neovim LSP
+" > neovim/nvim-lspconfig
+call s:hi("LspDiagnosticsDefaultWarning", s:nord13_gui, "", s:nord13_term, "", "", "")
+call s:hi("LspDiagnosticsDefaultError" , s:nord11_gui, "", s:nord11_term, "", "", "")
+call s:hi("LspDiagnosticsDefaultInformation" , s:nord8_gui, "", s:nord8_term, "", "", "")
+call s:hi("LspDiagnosticsDefaultHint" , s:nord10_gui, "", s:nord10_term, "", "", "")
+call s:hi("LspDiagnosticsUnderlineWarning" , s:nord13_gui, "", s:nord13_term, "", "undercurl", "")
+call s:hi("LspDiagnosticsUnderlineError" , s:nord11_gui, "", s:nord11_term, "", "undercurl", "")
+call s:hi("LspDiagnosticsUnderlineInformation" , s:nord8_gui, "", s:nord8_term, "", "undercurl", "")
+call s:hi("LspDiagnosticsUnderlineHint" , s:nord10_gui, "", s:nord10_term, "", "undercurl", "")
 
 " GitGutter
 " > airblade/vim-gitgutter