[css-display-3] Clarify dates on changes.

Author: fantasai

css-display-3/Overview.bs

@@ -1895,7 +1895,7 @@ Changes Since 2020 Candidate Recommendation</h3>
 			Updated references to <a href="https://www.w3.org/TR/css-grid/">CSS Grid Layout</a>.
 	</ul>
 
-	Changes since the <a href="https://www.w3.org/TR/2020/CR-css-display-3-20200519/">19 May 2020 Candidate Recommendation</a>
+	Previous changes since the <a href="https://www.w3.org/TR/2020/CR-css-display-3-20200519/">19 May 2020 Candidate Recommendation</a>
 	consist only of minor editorial clarifications and cross-linking improvements.
 
 <h3 id="changes-2019">