Parsing with format object parameter doesn't work

**Describe the bug**
I'm using the following plugins:
```ts
import * as customParseFormat from 'dayjs/plugin/customParseFormat';
import * as weekday from 'dayjs/plugin/weekday';
import * as localizedFormat from 'dayjs/plugin/localizedFormat';
import * as DAYJS_LOCALE_DE from 'dayjs/locale/de';

dayjs.extend(customParseFormat);
dayjs.extend(weekday);
dayjs.extend(localizedFormat);
dayjs.locale(DAYJS_LOCALE_DE);
```

The [TypeScript declarations](https://github.com/iamkun/dayjs/blob/dev/types/index.d.ts#L5-L14) (extract below) suggest that the `dayjs()` function accepts the second parameter in the object form `{ locale?: string, format?: string, utc?: boolean }`.

```ts
declare function dayjs (date?: dayjs.ConfigType): dayjs.Dayjs
declare function dayjs (date?: dayjs.ConfigType, format?: dayjs.OptionType, strict?: boolean): dayjs.Dayjs
declare function dayjs (date?: dayjs.ConfigType, format?: dayjs.OptionType, locale?: string, strict?: boolean): dayjs.Dayjs

declare namespace dayjs {
export type ConfigType = string | number | Date | Dayjs
export type OptionType = { locale?: string, format?: string, utc?: boolean } | string | string[]
...
}
```

However, calling `dayjs('8. Dez 2020 15:22', { format: 'D. MMM YYYY HH:mm'})` returns an invalid date whereas `dayjs('8. Dez 2020 15:22', 'D. MMM YYYY HH:mm')` returns a parsed date.

**Expected behavior**
Calling `dayjs('8. Dez 2020 15:22', { format: 'D. MMM YYYY HH:mm'})` returns a parsed date.

**Information**
- Day.js Version 1.9.7
- OS: Windows
- Browser Firefox 84, Chrome 87
- Time zone: GMT+1

Start with the overloads in types/index.d.ts and the customParseFormat plugin entry point, then reproduce the German-locale example using the object-form format parameter. Compare it with the string-format call and add or update a focused parsing test; done means the object form returns a valid parsed date.

Written by the indexing model from the issue text.