Downgrade Plug to 1.10.x, revert upload_limit tuple to function change

This should fix setting the upload limit in the database as found in:
https://queer.hacktivis.me/notice/A8XUZp74Cg7eYNEMxU

This reverts commit 7d350b73f5.

lib/pleroma/web/endpoint.ex

@@ -102,7 +102,7 @@ defmodule Pleroma.Web.Endpoint do
   plug(Plug.Parsers,
     parsers: [
       :urlencoded,
-      {:multipart, length: Config.get([:instance, :upload_limit])},
+      {:multipart, length: {Config, :get, [[:instance, :upload_limit]]}},
       :json
     ],
     pass: ["*/*"],