**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/api.spec.js
describe('static api', function () {
  it('should have request method helpers', function () {
    expect(typeof axios.request).toEqual('function');
    expect(typeof axios.get).toEqual('function');
    expect(typeof axios.head).toEqual('function');
    expect(typeof axios.options).toEqual('function');
    expect(typeof axios.delete).toEqual('function');
    expect(typeof axios.post).toEqual('function');
    expect(typeof axios.put).toEqual('function');
    expect(typeof axios.patch).toEqual('function');
  });
  it('should have promise method helpers', function () {
    var promise = axios('/test');
    expect(typeof promise.then).toEqual('function');
    expect(typeof promise.catch).toEqual('function');
  });
  it('should have defaults', function () {
    expect(typeof axios.defaults).toEqual('object');
    expect(typeof axios.defaults.headers).toEqual('object');
  });
  it('should have interceptors', function () {
    expect(typeof axios.interceptors.request).toEqual('object');
    expect(typeof axios.interceptors.response).toEqual('object');
  });
  it('should have all/spread helpers', function () {
    expect(typeof axios.all).toEqual('function');
    expect(typeof axios.spread).toEqual('function');
  });