Wait for entered tag before submitting

The changed spec was failing from time to time. This change seems to
make it stable. It may be worth moving tag entering into a helper that
verifies that the tag was entered (waits for it).

spec/features/admin/shipping_methods_spec.rb

@@ -104,7 +104,7 @@ feature 'shipping methods' do
       check "shipping_method_shipping_categories_"
       find(:css, "tags-input .tags input").set "local\n"
       within(".tags .tag-list") do
-        expect(page).to have_css '.tag-item'
+        expect(page).to have_css '.tag-item', text: "local"
       end
 
       click_button I18n.t("actions.create")