.diff return incorrect value when comparing 1st of Feb

[jckh1234]

Describe the bug
When using .diff()

To Reproduce
Go to http://jsfiddle.net/n4fodzr0/
console.log(new moment("2021-02-01").diff("1960-01-31", "years", true))
//output: 60.998587570621474
console.log(new moment("2021-01-31").diff("1960-01-31", "years", true))
//output: 61

Expected behavior
Expected the first line of code a value larger than 61

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• Browser Chrome
• Version 2.21

Moment-specific environment
"Mon Feb 01 2021 23:17:23 GMT+0800 (China Standard Time)"
"2/1/2021, 11:17:23 PM"
-480
"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.104 Safari/537.36"
"2.2.1"