UTC compare returns wrong result

**Describe the bug**

The compare result goes wrong when using `utc` to transform dayjs first.

**Expected behavior**

Works fine with or without using `utc`

**Information**
- Day.js Version 1.8.24
- OS: Mac & Windows
- Browser chrome 80
- Time zone: GMT+0800 (China Standard Time)

```js
const dayjs = require('dayjs')
const utc = require('dayjs/plugin/utc')

dayjs.extend(utc)

let formatter = 'YYYY-MM-DD HH:mm:ss'

const result = dayjs('2020-04-23T15:00:00').utc().add(1, 'hour').isAfter(dayjs('2020-04-23T09:00:00'))

console.log(dayjs('2020-04-23T15:00:00').utc().format(formatter))
console.log(dayjs('2020-04-23T09:00:00').format(formatter))

console.log(result) // true. Actuall, it should return false
```

Start by running the supplied reproduction with the dayjs/plugin/utc entry point and compare the UTC-transformed value with the local value. Trace the comparison and add operation involved in the example; done means the reported expression returns false and comparison behavior is consistent with and without utc.

Written by the indexing model from the issue text.