Fix broken HTML anchor in the Rationale documentation (#7783)

The italic Markdown formatting is included in the automatically
generated ID, so it must be present in the references as well.

docs/rationale.md

@@ -187,7 +187,7 @@ This practice is also common in [standard] which uses a semicolon-free style.
 
 The [`--print-width`](options.md#print-width) is more of a guideline to Prettier than a hard rule. It generally means “try to make lines this long, go shorter if needed and longer in special cases.”
 
-There are some edge cases, such as really long string literals, regexps, comments and variable names, which cannot be broken across lines (without using code transforms which [Prettier doesn’t do](#what-prettier-is-not-concerned-about)). Or if you nest your code 50 levels deep your lines are of course going to be mostly indentation :)
+There are some edge cases, such as really long string literals, regexps, comments and variable names, which cannot be broken across lines (without using code transforms which [Prettier doesn’t do](#what-prettier-is-_not_-concerned-about)). Or if you nest your code 50 levels deep your lines are of course going to be mostly indentation :)
 
 Apart from that, there are a few cases where Prettier intentionally exceeds the print width.