rpc: use class methods on nvim-0.11 (fix #211)

Author: mochaaP

lua/null-ls/rpc.lua

@@ -132,9 +132,14 @@ M.start = function(dispatchers)
         return handle(method, params, nil, true)
     end
 
+    local use_class_method = vim.fn.has("nvim-0.11") == 1
     return {
-        request = request,
-        notify = notify,
+        request = use_class_method and request or function(_, ...)
+            request(...)
+        end,
+        notify = use_class_method and notify or function(_, ...)
+            notify(...)
+        end,
         is_closing = function()
             return stopped
         end,