[css-writing-modes-3] Fix typo #4293 (#4294)

Author: frogcat

css-writing-modes-3/Overview.bs

@@ -2506,7 +2506,7 @@ Privacy and Security Considerations {#priv-sec}
 
   <h3 class="no-num" id="changes-20190730">
   Changes since the <a href="https://www.w3.org/TR/2019/CR-css-writing-modes-3-20190730/">July
-  2091 CSS Writing Modes Module Level 3 Candidate Recommendation</a></h3>
+  2019 CSS Writing Modes Module Level 3 Candidate Recommendation</a></h3>
 
   <ul>
     <li>Added back accidentally-dropped rules for sizing [=orthogonal flows=].