Fix link to `lib/defaults/index.js `

[ojj1123]

close: #87

TO-DO

• This PR(#88) is too old and no longer being edited.
• I have modified the url for all languages.
• AS-IS https://github.com/axios/axios/blob/master/lib/defaults.js#L28

[lib/defaults.js](https://github.com/axios/axios/blob/master/lib/defaults.js#L28)

• TO-BE https://github.com/axios/axios/blob/v1.x/lib/defaults/index.js#L40

[`lib/defaults/index.js`](https://github.com/axios/axios/blob/v1.x/lib/defaults/index.js#L40)