updated properties of extensions

Mailer.php

@@ -66,6 +66,10 @@ use yii\mail\BaseMailer;
  *
  * @see http://swiftmailer.org
  *
+ * @property array|\Swift_Mailer $swiftMailer Swift mailer instance or array configuration. This property is
+ * read-only.
+ * @property array|\Swift_Transport $transport This property is read-only.
+ *
  * @author Paul Klimov <klimov.paul@gmail.com>
  * @since 2.0
  */

Message.php

@@ -16,7 +16,8 @@ use yii\mail\BaseMessage;
  * @see Mailer
  *
  * @method Mailer getMailer() returns mailer instance.
- * @property \Swift_Message $swiftMessage vendor message instance.
+ *
+ * @property \Swift_Message $swiftMessage Swift message instance. This property is read-only.
  *
  * @author Paul Klimov <klimov.paul@gmail.com>
  * @since 2.0