Fix TOC following review recos

Author: rambk

articles/expressroute/TOC.yml

@@ -71,7 +71,7 @@
     - name: Private Peering
       href: designing-for-disaster-recovery-with-expressroute-privatepeering.md
     - name: Using VPN as a backup
-      href: using-s2s-vpn-as-a-backup-for-expressroute-privatepeering.md      
+      href: use-s2s-vpn-as-backup-for-expressroute-privatepeering.md      
 - name: How-to guides
   items:
   - name: Create and modify a circuit