Update 'IsAdmin' flag to use correct syntax 'Admin'

The first example uses a flag -IsAdmin which does not exist. Updated to the correct syntax.

Author: lfoust

src/ResourceManager/ServiceFabric/Commands.ServiceFabric/help/Add-AzureRmServiceFabricClientCertificate.md

@@ -46,7 +46,7 @@ Use **Add-AzureRmServiceFabricClientCertificate** to add a common name and issue
 
 ### Example 1
 ```
-PS c:> Add-AzureRmServiceFabricClientCertificate -ResourceGroupName 'Group1' -Name 'Contoso01SFCluster' -Thumbprint 5F3660C715EBBDA31DB1FFDCF508302348DE8E7A -IsAdmin
+PS c:> Add-AzureRmServiceFabricClientCertificate -ResourceGroupName 'Group1' -Name 'Contoso01SFCluster' -Thumbprint 5F3660C715EBBDA31DB1FFDCF508302348DE8E7A -Admin
 ```
 
 This command will add the certificate with thumbprint '5F3660C715EBBDA31DB1FFDCF508302348DE8E7A' to the cluster, so the client can use the certificate as admin to communicate with the cluster.