**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
lib/core/Axios.js
this.defaults = instanceConfig;
  this.interceptors = {
    request: new InterceptorManager(),
    response: new InterceptorManager()
  };
}
/**
 * Dispatch a request
 *
 * @param {Object} config The config specific for this request (merged with this.defaults)
 */
Axios.prototype.request = function request(configOrUrl, config) {
  
  
  if (typeof configOrUrl === 'string') {
    config = config || {};
    config.url = configOrUrl;
  } else {
    config = configOrUrl || {};