Fix: flaky test, wait for server-side call to complete.

Author: dblock

spec/integration/teams_spec.rb

@@ -60,6 +60,7 @@
       it 'includes optional parameter' do
         expect(SlackRubyBotServer::Service.instance).to receive(:create!).with(instance_of(Team), { state: 'property' })
         visit '/?v2&code=code&state=property'
+        expect(page.find('#messages')).to have_content 'Team successfully registered!'
       end
     end
     context 'homepage' do