Handle escaped backticks is wrong when dedent used as function

[sirian]

dedent("\\`") === "`"

Bug in this line https://github.com/dmnd/dedent/blob/master/dedent.js#L17

[JoshuaKGoldberg]

👋 @sirian! Recognizing this is a few years old - if it's still something you have both time and interest for, I posted a proposal for adding an option in #63. Seeking input if you have time!