Update virtualNetworkGateway.json

Change description to match others

Author: litchiyangMSFT

specification/network/resource-manager/Microsoft.Network/stable/2020-07-01/virtualNetworkGateway.json

@@ -2781,7 +2781,7 @@
         "name",
         "type"
       ],
-      "description": "The extended location of type local virtual network gateway."
+      "description": "ExtendedLocation complex type."
     },
     "VirtualNetworkGateway": {
       "properties": {