update tsserver LSP to ts_ls

neovim/nvim-lspconfig#3232 (comment)
tsserver was suddenly renamed to ts_ls.

Author: schistos

init.lua

@@ -581,7 +581,7 @@ require('lazy').setup({
         --    https://github.com/pmizio/typescript-tools.nvim
         --
         -- But for many setups, the LSP (`tsserver`) will work just fine
-        tsserver = {},
+        ts_ls = {},
         html = {},
         cssls = {},
         clangd = {},