[css-variables] Fix deadline.

Author: tabatkins

css-variables/Overview.html

@@ -77,7 +77,7 @@ <h2 id="status" class="no-num no-toc no-ref">Status of this document</h2>
    persons are encouraged to review this document and <strong>send comments
    to the <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a>
    mailing list</strong> as described above. The <strong>deadline for
-   comments</strong> is <strong>13 May 2013</strong>.</p></div>
+   comments</strong> is <strong>13 June 2013</strong>.</p></div>
 <div data-fill-with="at-risk"></div>
 
 <h2 id="contents" class="no-num no-toc no-ref">Table of contents</h2>