parseHeaders = rawHeaders => {
  const parsed = {};
  let key;
  let val;
  let i;

  rawHeaders && rawHeaders.split('\n').forEach(function parser(line) {
    i = line.indexOf(':');
    key = line.substring(0, i).trim().toLowerCase();
    val = line.substring(i + 1).trim();

    if (!key || (parsed[key] && ignoreDuplicateOf[key])) {
      return;
    }

    if (key === 'set-cookie') {
      if (parsed[key]) {
        parsed[key].push(val);
      } else {
        parsed[key] = [val];
      }
    } else {
      parsed[key] = parsed[key] ? parsed[key] + ', ' + val : val;
    }
  });

  return parsed;
}
Parse headers into an object

```
Date: Wed, 27 Aug 2014 08:58:49 GMT
Content-Type: application/json
Connection: keep-alive
Transfer-Encoding: chunked
```

@param {String} rawHeaders Headers needing to be parsed

@returns {Object} Headers parsed into an object