[css-transitions-1] Update changelog

Author: birtles

css-transitions-1/Overview.bs

@@ -1351,6 +1351,14 @@ dated 30 November 2017</a>:
     since it was not implemented by any user agent
     and likely to cause compatibility problems.
 
+*   Moved the definitions of how properties interpolate to
+    <a
+    href="https://drafts.csswg.org/web-animations-1/#animating-properties">Web
+    Animations">Web Animations</a>
+    and
+    <a href="https://drafts.csswg.org/css-values-4/#combining-values">CSS Values
+    and Units</a>.
+
 For more details on these changes, see the version control
 <a href="https://github.com/w3c/csswg-drafts/commits/master/css-transitions-1/Overview.bs">change log</a>.