Inconsistent behavior of dayjs.max and dayjs.min

**Describe the bug**
```
const dates = [dayjs()];

dayjs.max(...dates); // == null
dayjs.max(dates); // == date
```
And the same for dayjs.min.
I think it's weird that it returns different values for different types of arguments passing

**Expected behavior**
I think it shoud return datejs instance in both cases

**Information**
- Day.js Version 1.8.28
- OS: MacOS
- Browser chrome 87

Start by reproducing the reported dayjs.max and dayjs.min calls with a one-item array passed both directly and via spread. Then inspect the max/min API implementation and verify that both invocation forms return a Day.js instance, with tests covering each form.

Written by the indexing model from the issue text.