**Describe the bug**
When using https://github.com/axios/axios/pull/1712 example and adding baseURL in config, baseURL seems to not be used.

**To Reproduce**

```js
const axios = require("axios");
const fakeConfig = {
  method: "post",
  url: "/user/12345",
  baseURL: "/foo"
};
console.log(axios.getUri(fakeConfig));
```

**Expected behavior**
`axios.getUri` should return `/foo/user/12345`.

If this expected behavior seems right, I can work on a fix.

**Environment:**
 - Axios Version: 0.19.0
 - OS: Linux, Windows
 - Browser Chrome but also happen on Firefox and node
test/specs/instance.spec.js
afterEach(function () {
    jasmine.Ajax.uninstall();
  });
  it('should have the same methods as default instance', function () {
    var instance = axios.create();
    for (var prop in axios) {
      if ([
        'Axios',
        'create',
        'Cancel',
        'CancelToken',
        'isCancel',
        'all',
        'spread',
        'isAxiosError',
        'VERSION',
        'default'].indexOf(prop) > -1) {
        continue;
      }
      expect(typeof instance[prop]).toBe(typeof axios[prop]);
    }
  });
  it('should make an http request without verb helper', function (done) {
    var instance = axios.create();
    instance('/foo');
    getAjaxRequest().then(function (request) {
      expect(request.url).toBe('/foo');
      done();
    });
  });