Clarify TLS Root cert for IoT Hub

Baltimore CyberTrust root CA is no longer needed. So only "two" root certificates need to be trusted for now.

Author: nkgami

articles/iot-hub/iot-hub-tls-support.md

@@ -47,7 +47,7 @@ After a successful TLS handshake, IoT Hub can authenticate a device using a symm
 
 During a TLS handshake, IoT Hub presents RSA-keyed server certificates to connecting clients. All IoT hubs in the global Azure cloud use the TLS certificate issued by the DigiCert Global Root G2. 
 
-We strongly recommend that all devices trust the following three root CAs: 
+We strongly recommend that all devices trust the following two root CAs: 
 
 * DigiCert Global G2 root CA
 * Microsoft RSA root CA 2017