use lua way to handle color scheme errors

lua/user/colorscheme.lua

@@ -1,8 +1,7 @@
-vim.cmd [[
-try
-  colorscheme darkplus
-catch /^Vim\%((\a\+)\)\=:E185/
-  colorscheme default
-  set background=dark
-endtry
-]]
+local colorscheme = "default"
+
+local status_ok, _ = pcall(vim.cmd, "colorscheme " .. colorscheme)
+if not status_ok then
+  vim.notify("colorscheme " .. colorscheme .. " not found!")
+  return
+end