nvim: lua: completion: Enable treesitter completion with nvim-compe

compe recently added completion support with treesitter. Enable it.

nvim/.config/nvim/lua/modules/completion.lua

@@ -17,6 +17,7 @@ require'compe'.setup {
     nvim_lua      = true;
     spell         = true;
     tags          = true;
+    treesitter    = true;
     snippets_nvim = false;
     vsnip         = false;
   };