syntax: fix Markdown for ASCII word class rendering

Author: BurntSushi

regex-syntax/src/lib.rs

@@ -381,7 +381,7 @@ pub fn try_is_word_character(
 /// Returns true if and only if the given character is an ASCII word character.
 ///
 /// An ASCII word character is defined by the following character class:
-/// `[_0-9a-zA-Z]'.
+/// `[_0-9a-zA-Z]`.
 pub fn is_word_byte(c: u8) -> bool {
     match c {
         b'_' | b'0'..=b'9' | b'a'..=b'z' | b'A'..=b'Z' => true,