IcmpPing does not emit ToPort value

[richardnagle]

Using the IcmpPing class like so:

 sg.addIngressRule(new AnyIPv4(), new IcmpPing(), "Allow Ping");

Creates the following output from cdk synth

          {
            "CidrIp": "0.0.0.0/0",
            "Description": "Allow Ping",
            "FromPort": 8,
            "IpProtocol": "icmp"
          }

This is missing the ToPort value and will fail when cdk deploy is executed.