use lua way to handle color scheme errors

lua/user/colorscheme.lua

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