Fix link to extensions (dart-lang#2717)

* Fix link to extensions

* Rebuild AOT templates

Co-authored-by: Janice Collins <jcollins@google.com>

Author: geisterfurz007

lib/src/generator/templates.aot_renderers_for_html.dart

@@ -9640,7 +9640,7 @@ String renderSidebarForLibrary<T extends _i17.Documentable>(
       buffer.write('''
   <li class="section-title"><a href="''');
       buffer.write(context1.href.toString());
-      buffer.write('''#extension">Extensions</a></li>''');
+      buffer.write('''#extensions">Extensions</a></li>''');
       var context4 = context1.publicExtensionsSorted;
       if (context4 != null) {
         for (var context5 in context4) {

lib/templates/html/_sidebar_for_library.html

@@ -8,7 +8,7 @@
   {{/hasPublicClasses}}
 
   {{#hasPublicExtensions}}
-  <li class="section-title"><a href="{{{href}}}#extension">Extensions</a></li>
+  <li class="section-title"><a href="{{{href}}}#extensions">Extensions</a></li>
   {{#publicExtensionsSorted}}
   <li>{{{ linkedName }}}</li>
   {{/publicExtensionsSorted}}