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#### Summary

set baseURL in interceptors is not working.

```
const service = axios.create({
  baseURL: 'http://localhost/'
});

service.interceptors.request.use(config => {

  config.baseURL = 'dd'
  console.log(config.url) // output :  http://localhost/././../

  return config;
}, error => {
  // Do something with request error
  console.error(error); // for debug
  Promise.reject(error);
})
```

#### Context

- axios version: *e.g.: v0.16.2*
- Environment: *e.g.: node vv8.0.0, chrome  59.0.3071.86, macOS 10.12*

lib/core/Axios.js
'use strict';
var defaults = require('./../defaults');
var utils = require('./../utils');
var InterceptorManager = require('./InterceptorManager');
var dispatchRequest = require('./dispatchRequest');
var isAbsoluteURL = require('./../helpers/isAbsoluteURL');
var combineURLs = require('./../helpers/combineURLs');
/**
 * Create a new instance of Axios
 *
 * @param {Object} instanceConfig The default config for the instance
 */
function Axios(instanceConfig) {