Revise lab description and adjust difficulty level

Updated lab description and reduced level from 500 to 400.

Author: staleycyn

Instructions/Exercises/M06-Unit 9 Secure your virtual hub using Azure Firewall Manager.md

@@ -1,12 +1,9 @@
 ---
 lab:
   title: M06-Unit 9 Secure your virtual hub using Azure Firewall Manager
-  description: In this exercise, you will create the spoke virtual network and create
-    a secured virtual hub, then you will connect the hub and spoke virtual networks
-    and route traffic to your hub. Next you will deploy the workload servers, then
-    create a firewall policy and secure your hub, and finally you will test the firewall.
+  description: Create and configure Azure Firewall Manager. 
   duration: 35 minutes
-  level: 500
+  level: 400
   islab: true
   primarytopics:
   - Azure