[css-transitions-1] Fix link to commit history.

Modeled on change in #11965.

Author: dbaron

css-transitions-1/Overview.bs

@@ -1383,7 +1383,7 @@ For changes in earlier working drafts:
      ChangeLog</a> for changes in previous working drafts.
 1.   For more details on these changes, see the version control change logs,
      which are split in many parts because of file renaming:
-     *   <a href="https://github.com/w3c/csswg-drafts/commits/master/css-transitions-1/Overview.bs">change log since 2017 October 12</a>,
+     *   <a href="https://github.com/w3c/csswg-drafts/commits/main/css-transitions-1/Overview.bs">change log since 2017 October 12</a>,
      *   <a href="https://hg.csswg.org/drafts/log/tip/css-transitions/Overview.bs">change log from 2015 January 26 to 2017 October 12</a>,
      *   <a href="https://hg.csswg.org/drafts/log/tip/css-transitions/Overview.src.html">change log from 2013 March 28 to 2015 January 26</a>,
      *   <a href="https://hg.csswg.org/drafts/log/tip/css3-transitions/Overview.src.html">change log before 2013 March 28</a>.