home: vim: add 'cmp_luasnip'

I had forgotten to add it even though I configured it as a source...

home/vim/default.nix

@@ -78,6 +78,7 @@ in
       cmp-nvim-lua # NeoVim lua API
       cmp-path # Path name suggestions
       cmp-under-comparator # Sort items that start with '_' lower
+      cmp_luasnip # Snippet suggestions from LuaSnip
 
       # UX improvements
       dressing-nvim # Integrate native UI hooks with Telescope etc...