Wrong loading of plugins/locale breaks the app.

**Describe the bug**
Loading plugins before and then loading the locale for `en` breaks the app.

**Expected behavior**
Should work correctly without any error.

**Information**
- Day.js Version - 1.9.6
- OS: Mac
- Browser Chrome

Let's say we have code like this
```js
dayjs.extend(advancedFormat);
dayjs.locale(require('dayjs/locale/en'))

// Then when you try to do
dayjs().format('dddd, MMM Do, YYYY');
```
It breaks with an error `d.ordinal` is not a function. It is because there is no `ordinal` property in `en.js` file. More specifically this function https://github.com/iamkun/dayjs/blob/dev/src/plugin/advancedFormat/index.js#L6 should be moved to `en.js` file.

Repro - https://codesandbox.io/s/elegant-christian-hbsr7?file=/src/index.js

Happy to submit a PR.

Start with src/plugin/advancedFormat/index.js and the en.js locale file referenced in the issue, then reproduce the failure using the linked CodeSandbox or the supplied formatting example. Verify that loading advancedFormat before the English locale no longer causes d.ordinal to be undefined when formatting the example date.

Written by the indexing model from the issue text.