title: How to add progress event to react-native-fetch-polyfill
body: <p>I am trying to use <code>react-native-fetch-polyfill</code> becouse of <code>timeout</code> feature for fetch requests but can't implement <code>onProgress</code> event:</p>
  
  <pre><code>fetch('https://jsonplaceholder.typicode.com/posts', {
      method: 'POST',
      body: JSON.stringify({
        title: 'foo',
        body: 'bar',
        userId: 1
      }),
      headers: {
        "Content-type": "application/json; charset=UTF-8"
      }
    })
    .then(function(data) {
      console.log(data);
    })
    .catch(function(error) {
      console.log('Fetch Error :-S', error);
    });
  </code></pre>
  
  <p>I don't know where to add:</p>
  
  <pre><code>onUploadProgress: function (progressEvent)
  </code></pre>