I have axios@0.15.2

If this HTML is run, some requests will be cancelled by Chrome:

    <html>
    <head>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/axios/0.15.2/axios.js"></script>
    </head>
        <script>
        var promises = [];
        window.onload = function() {
            for (var i = 0; i < 4; i++) {
                var promise = axios.get('some url which causes ERR_CONNECTION_CLOSED');
                promises.push(promise);
            }
        }
       </script>
    </html>

![Cancelled](https://cloud.githubusercontent.com/assets/4506837/20349972/9123cef0-ac2e-11e6-93db-0ec66f205382.png)

But promises which turned into cancelled request won't be fulfilled:

![notfulfilled](https://cloud.githubusercontent.com/assets/4506837/20350023/d2146c4e-ac2e-11e6-89bc-983233628d09.png)

lib/adapters/xhr.js
if (xsrfValue) {
        requestHeaders[config.xsrfHeaderName] = xsrfValue;
      }
    }
    
    if ('setRequestHeader' in request) {
      utils.forEach(requestHeaders, function setRequestHeader(val, key) {
        if (typeof requestData === 'undefined' && key.toLowerCase() === 'content-type') {
          
          delete requestHeaders[key];
        } else {
          
          request.setRequestHeader(key, val);
        }
      });
    }
    
    if (config.withCredentials) {
      request.withCredentials = true;
    }
    
    if (config.responseType) {
      try {
        request.responseType = config.responseType;
      } catch (e) {
        
        
        if (config.responseType !== 'json') {
          throw e;
        }