Fix a deprecated function in Elixir docs (#9997)

See getsentry/sentry-elixir#730.

Author: whatyouhide

docs/platforms/elixir/integrations/plug_and_phoenix/index.mdx

@@ -62,7 +62,7 @@ defmodule MyAppWeb.ErrorView do
         ~E"""
         <script src="https://browser.sentry-cdn.com/5.9.1/bundle.min.js" integrity="sha384-/x1aHz0nKRd6zVUazsV6CbQvjJvr6zQL2CHbQZf3yoLkezyEtZUpqUNnOLW9Nt3v" crossorigin="anonymous"></script>
         <script>
-          Sentry.init({ dsn: '<%= Sentry.Config.dsn() %>' });
+          Sentry.init({ dsn: '<%= Sentry.get_dsn() %>' });
           Sentry.showReportDialog(<%= raw opts %>)
         </script>
         """