FIX: Allow IE script to load with a CDN

A proper fix would involve it being precompiled like other assets, but
due to the conditional nature of the resource this is more complicated.

For now this is better than IE being broken.

plugins/discourse-internet-explorer/plugin.rb

@@ -47,7 +47,7 @@ after_initialize do
   # to be loaded before other files
   register_html_builder('server:before-script-load') do |controller|
     if BrowserDetection.browser(controller.request.env['HTTP_USER_AGENT']) == :ie
-      path = controller.helpers.script_asset_path('/plugins/discourse-internet-explorer/js/ie')
+      path = "#{Discourse.base_uri}/plugins/discourse-internet-explorer/js/ie.js"
 
       <<~JAVASCRIPT
         <script src="#{path}"></script>