add support for retrieving wellsaid speech credential

lib/session/call-session.js

@@ -264,6 +264,12 @@ class CallSession extends Emitter {
             region: credential.region
           };
         }
+        else if ('wellsaid' === vendor) {
+          return {
+            speech_credential_sid: credential.speech_credential_sid,
+            api_key: credential.api_key
+          };
+        }
       }
       else {
         writeAlerts({