Custom toString() so that secrets don't get logged

spring-cloud-kubernetes-config/src/main/java/org/springframework/cloud/kubernetes/config/SecretsPropertySource.java

@@ -99,6 +99,10 @@ public class SecretsPropertySource extends KubernetesPropertySource {
 		return result;
 	}
 
+	@Override public String toString() {
+		return getClass().getSimpleName()
+	}
+
 	// *****************************
 	// Helpers
 	// *****************************