Currently, if you use axios with async / await, you get a stack trace like this:

```
Request failed with status code 500
    at createError (/Users/rmenezes/code/seedfi/web/node_modules/axios/lib/core/createError.js:16:15)
    at settle (/Users/rmenezes/code/seedfi/web/node_modules/axios/lib/core/settle.js:17:12)
    at IncomingMessage.handleStreamEnd (/Users/rmenezes/code/seedfi/web/node_modules/axios/lib/adapters/http.js:237:11)
    at IncomingMessage.emit (events.js:208:15)
    at IncomingMessage.EventEmitter.emit (domain.js:471:20)
    at endReadableNT (_stream_readable.js:1154:12)
    at processTicksAndRejections (internal/process/task_queues.js:77:11
```

It doesn't show you much about *what* called Axios., which makes debugging quite difficult!

This is because `settle` calls `createError`:
https://github.com/axios/axios/blob/master/lib/core/settle.js#L12-L24

Which creates a new error with a brand new stack trace:
https://github.com/axios/axios/blob/master/lib/core/createError.js#L15-L18

Perhaps we can fix this by creating an error before the request goes out and stitching it to the new error's stack trace?
test/unit/adapters/http.js
});
  });
  it('should allow passing JSON', function (done) {
    var data = {
      firstName: 'Fred',
      lastName: 'Flintstone',
      emailAddr: 'fred@example.com'
    };
    server = http.createServer(function (req, res) {
      res.setHeader('Content-Type', 'application/json');
      res.end(JSON.stringify(data));
    }).listen(4444, function () {
      axios.get('http://localhost:4444/').then(function (res) {
        assert.deepEqual(res.data, data);
        done();
      }).catch(done);
    });
  });
  it('should allow passing JSON with BOM', function (done) {
    var data = {
      firstName: 'Fred',
      lastName: 'Flintstone',
      emailAddr: 'fred@example.com'
    };
    server = http.createServer(function (req, res) {
      res.setHeader('Content-Type', 'application/json');
      var bomBuffer = Buffer.from([0xEF, 0xBB, 0xBF])
      var jsonBuffer = Buffer.from(JSON.stringify(data));
      res.end(Buffer.concat([bomBuffer, jsonBuffer]));
    }).listen(4444, function () {