adding right powershell command

Add-AzureApplicationGatewayRequestRoutingRule      <-- incorrect
Add-AzureRmApplicationGatewayRequestRoutingRule <--corrected command

Author: chunsiongtan

src/ResourceManager/Network/Commands.Network/help/Add-AzureRmApplicationGatewayRequestRoutingRule.md

@@ -39,7 +39,7 @@ The **Add-AzureRmApplicationGatewayRequestRoutingRule** cmdlet adds a request ro
 ### Example 1: Add a request routing rule to an application gateway
 ```
 PS C:\>$AppGw = Get-AzureRmApplicationGateway -Name "ApplicationGateway01" -ResourceGroupName "ResourceGroup01"
-PS C:\> $Appgw = Add-AzureApplicationGatewayRequestRoutingRule -ApplicationGateway $AppGw -Name "Rule01" -RuleType Basic -BackendHttpSettings $Setting -HttpListener $Listener -BackendAddressPool $Pool
+PS C:\> $Appgw = Add-AzureRmApplicationGatewayRequestRoutingRule -ApplicationGateway $AppGw -Name "Rule01" -RuleType Basic -BackendHttpSettings $Setting -HttpListener $Listener -BackendAddressPool $Pool
 ```
 
 The first command gets the application gateway and stores it in the $AppGw variable.