Bold italic text convertion to markdown error

[Ynjxsjmh]

If there is a text with both bold and italic, Copycat will convert them to ***with both bold and italics***. It should be _**with both bold and italics**_ or __*with both bold and italics*__ etc.

Test link: sentence 是对问题状态的定义和状态转移方程的定义。 in https://www.zhihu.com/question/23995189/answer/35324479

MD style: GFM Copycat version: 2.4.2