title: Specify response.request.responseURL in moxios
body: <p>I'm currently trying to write some functionality that requires the <code>response.request.responseURL</code> value to be set when axios handles the response. However, I can't seem to set this value with moxios. Here's what my test looks like:</p>
  
  <pre><code>it('resets list selection if input contents were replaced', (done) =&gt; {
      component.currently_selected_list_value = 10;
      component.last_called_url = 'henkiehoutman';
  
      let input = domElt.querySelector('input');
      ReactTestUtils.Simulate.change(input);
  
      moxios.wait(() =&gt; {
          let request = moxios.requests.mostRecent();
          request.respondWith({
              status: 200,
              response: [{
                  customer_info_customers: ['', '', '', '', ''],
                  domain_info_customers: {},
              }],
              request: {responseURL: 'banaan'}
          }).then(() =&gt; {
              // The contents were replaced, so it's best to forget whatever our selection was.
              expect(component.currently_selected_list_value).toEqual(-1);
              done();
          });
      });
  });
  </code></pre>
  
  <p>This is what my actual application looks like:</p>
  
  <pre><code>onChange (event) {
      return axios.get(
          this.props.ApiUrl + encodeURIComponent(event.target.value)
      ).then(
          (response) =&gt; {
              let response_url = response.request.responseURL;  // This is the value I want to set manually.
              if(this.shouldHandleResponse(response_url)){
                  this.last_called_url = response_url;
                  let data = response.data;
                  this.setState({results: data, dropdown: data.length &gt; 0});
  
                  if ( this.currently_selected_list_value &gt; max_index) {
                      this.currently_selected_list_value = max_index;
                  }
              }
          }
      );
  },
  </code></pre>
  
  <p>However, when I log what this value is, it just says <code>undefined</code>. And this is what the actual <code>response.request</code> value is (put it in a quote so it's a bit more readable):</p>
  
  <blockquote>
    <p>LOG: Request{resolve: function (a) { ... }, reject: function (a) { ... }, config: Object{adapter: function mockAdapter(config) { ... }, transformRequest: Object{0: ...}, transformResponse: Object{0: ...}, timeout: 0, xsrfCookieName: 'XSRF-TOKEN', xsrfHeaderName: 'X-XSRF-TOKEN', maxContentLength: -1, validateStatus: function validateStatus(status) { ... }, headers: Object{Accept: ..., X-CSRFToken: ...}, method: 'get', url: 'my_api_url/', data: undefined}, headers: Object{Accept: 'application/json, text/plain, <em>/</em>', X-CSRFToken: 'my_csrf_token'}, url: 'my_api_url/', timeout: 0, withCredentials: false, responseType: undefined}</p>
  </blockquote>
  
  <p>This breaks my application, because a <code>responseURL</code> should always be defined. It looks like it's overwriting the request I defined in moxios. This is not necessarily a bad thing, because I assume it needs these things to function properly. However, it would be nice if I could add some values to this request.</p>
  
  <p>So; How do I add a <code>responseURL</code> value to this request in moxios?</p>