Fix of a breaking change in the last version of vim-cmp

I'm not sure is it a bug or breaking change, but this config stopped work without specifying the `max_width` & `max_height`.
How to reproduce the error:
1. open a .lua file
2. print `fn` somewhere
3. pres `<tab>` twice

lua/user/cmp.lua

@@ -119,6 +119,9 @@ cmp.setup {
   },
   documentation = {
     border = { "╭", "─", "╮", "│", "╯", "─", "╰", "│" },
+    max_width = 50,
+    max_height = 80,
+
   },
   experimental = {
     ghost_text = false,