fix usage of Sprockets::Manifest in test

Author: rmosolgo

test/react/server_rendering/manifest_container_test.rb

@@ -7,7 +7,7 @@ def setup
     # Make a new manifest since assets weren't compiled before
     config = Rails.application.config
     path = File.join(config.paths['public'].first, config.assets.prefix)
-    new_manifest = Sprockets::Manifest.new(Rails.application.assets, path, config.assets.manifest)
+    new_manifest = Sprockets::Manifest.new(Rails.application.assets, path)
     Rails.application.assets_manifest = new_manifest
 
     @manifest_container = React::ServerRendering::ManifestContainer.new