Update main_menu.html

Fixes torchvision link in the menu.

Author: brianjo

_includes/main_menu.html

@@ -45,7 +45,7 @@
             <span class="dropdown-title docs-title">torchtext</span>
             <p></p>
           </a>
-          <a class="nav-dropdown-item" href="{{ site.baseurl }}/docs/stable/torchvision">
+          <a class="nav-dropdown-item" href="{{ site.baseurl }}/vision">
             <span class="dropdown-title docs-title">torchvision</span>
             <p></p>
           </a>