title: capybara poltergeist - override user agent
body: <p>Does somebody know how I could override the user agent of capybara poltergeist to a mobile one for testing?</p>
  
  <p>I found something about configuring that for the selenium webdriver:
  <a href="http://blog.plataformatec.com.br/2011/03/configuring-user-agents-with-capybara-selenium-webdriver/" rel="noreferrer">http://blog.plataformatec.com.br/2011/03/configuring-user-agents-with-capybara-selenium-webdriver/</a></p>
  
  <p>How this is possible in capybara poltergeist?</p>