title: How to set cookies in capybara with capybara-webkit
body: <p>I'm using capybara with capybara-webkit for testing, but I need to set some specific cookies.</p>
  
  <p>I'm so confused by it's document, and the source code.</p>
  
  <p>I did find a method here <a href="https://github.com/thoughtbot/capybara-webkit/blob/e6e2351a15cabf620152eb938e5cacb514fe1529/lib/capybara/webkit/browser.rb#L177" rel="nofollow">https://github.com/thoughtbot/capybara-webkit/blob/e6e2351a15cabf620152eb938e5cacb514fe1529/lib/capybara/webkit/browser.rb#L177</a></p>
  
  <p>But I really don't know what format should I use for the 'cookie' param in this method.</p>
  
  <p>If I have a cookie in json like this:</p>
  
  <pre><code>[
      {
          "domain": ".github.com",
          "expirationDate": 1453495731,
          "hostOnly": false,
          "httpOnly": false,
          "name": "__utma",
          "path": "/",
          "secure": false,
          "session": false,
          "storeId": "0",
          "value": "58162108.1841781874.1390418256.1390423639.1390423639.1",
          "id": 1
      },
      {
          "domain": ".github.com",
          "expirationDate": 1406191731,
          "hostOnly": false,
          "httpOnly": false,
          "name": "__utmz",
          "path": "/",
          "secure": false,
          "session": false,
          "storeId": "0",
          "value": "58162108.1390423639.1.1.utmcsr=developer.github.com|utmccn=(referral)|utmcmd=referral|utmcct=/",
          "id": 3
      },
      ... ...
  ]
  </code></pre>
  
  <p>How to modify the above into the correct acceptable string format for capybara-webkit? Can anyone give me an example?</p>