AzMon key vaults link fix

Author: lgayhardt

articles/azure-monitor/toc.yml

@@ -991,7 +991,7 @@
     - name: Azure Cosmos DB
       href: insights/cosmosdb-insights-overview.md
     - name: Key Vault
-      href: insights/key-vault-insights-overview.md
+      href: insights/key-vaults-insights-overview.md
     - name: Networks
       href: insights/network-insights-overview.md
     - name: Storage