Fix #376

plugin/cmp.lua

@@ -80,7 +80,8 @@ vim.cmd [[command! CmpStatus lua require('cmp').status()]]
 
 vim.cmd [[doautocmd <nomodeline> User cmp#ready]]
 
-vim.on_key(function(keys)
+if vim.on_key then
+  vim.on_key(function(keys)
     if keys == vim.api.nvim_replace_termcodes('<C-c>', true, true, true) then
       vim.schedule(function()
         if not api.is_suitable_mode() then
@@ -88,5 +89,6 @@ vim.on_key(function(keys)
         end
       end)
     end
-end, vim.api.nvim_create_namespace('cmp.plugin'))
+  end, vim.api.nvim_create_namespace('cmp.plugin'))
+end