chore: update doc website footer build status link (#197)

Author: iChenLei

_includes/footer.html

@@ -30,7 +30,7 @@ <h3 class="fancy">
             <ul>
                 <li><a href="https://github.com/chaijs/chai/issues" target="_blank">Issues</a></li>
                 <li><a href="https://groups.google.com/group/chaijs" target="_blank">Google Group</a></li>
-                <li><a href="https://travis-ci.org/#!/chaijs/chai" target="_blank">Build Status</a></li>
+                <li><a href="https://github.com/chaijs/chai/actions" target="_blank">Build Status</a></li>
             </ul>
         </div>
     </section>