abort to reconnect if isWrongStatusCodeOrContentType is true

Hi.

I found that this polyfill may not in accordance with the terms of the reconnection written [here][link1].

Although it's a very simple implements, I think it meets requirements.

Please review it and tell me your impressions.

I really thank you for creating such a useful polyfill. Thank you.


[link1]: http://www.w3.org/TR/eventsource/#processing-model "w3c"
I think, it is better to move more lines to the "else" branch:
```
if (isWrongStatusCodeOrContentType) {
  close();
} else {
  currentState = WAITING;
  xhr.abort();
  if (timeout !== 0) {
    clearTimeout(timeout);
    timeout = 0;
  }
  if (retry > initialRetry * 16) {
    retry = initialRetry * 16;
  }
  if (retry > MAXIMUM_DURATION) {
    retry = MAXIMUM_DURATION;
  }
  timeout = setTimeout(onTimeout, retry);
  retry = retry * 2 + 1;

  that.readyState = CONNECTING;
}
```