Multibyte characters on chunk boundaries get corrupted.

test/specs/headers.spec.js
}
      done();
    });
  });
  it('should use application/json when posting an object', function (done) {
    axios.post('/foo/bar', {
      firstName: 'foo',
      lastName: 'bar'
    });
    getAjaxRequest().then(function (request) {
      testHeaderValue(request.requestHeaders, 'Content-Type', 'application/json;charset=utf-8');
      done();
    });
  });
  it('should remove content-type if data is empty', function (done) {
    axios.post('/foo');
    getAjaxRequest().then(function (request) {
      testHeaderValue(request.requestHeaders, 'Content-Type', undefined);
      done();
    });
  });
  it('should preserve content-type if data is false', function (done) {
    axios.post('/foo', false);
    getAjaxRequest().then(function (request) {
      testHeaderValue(request.requestHeaders, 'Content-Type', 'application/x-www-form-urlencoded');
      done();
    });
  });
});