Fix Roadmap link

github has changed the way to reference the roadmap?

Author: Ludovic Rousseau

index.html

@@ -41,7 +41,7 @@
       </li>
       <li><a href="https://github.com/libusb/libusb">Development</a>
         <ul>
-          <li><a href="https://github.com/libusb/libusb/issues/milestones?direction=asc&sort=due_date">Roadmap</a></li>
+          <li><a href="https://github.com/libusb/libusb/milestones?direction=asc&sort=due_date&state=open">Roadmap</a></li>
           <li><a href="https://github.com/libusb/libusb/commits/master">Git Log</a></li>
           <li><a href="https://github.com/libusb/libusb/wiki#wiki-Accessing_the_Source">Git Access</a></li>
 <!--          <li><a href="#">Sending Patches</a></li> -->