Update MailerAssertionsTrait.php

`example.com` is the "official" domain for such things: http://example.com/

For the removal, see Codeception#120 (comment)

Author: ThomasLandauer

src/Codeception/Module/Symfony/MailerAssertionsTrait.php

@@ -48,7 +48,7 @@ public function seeEmailIsSent(int $expectedCount = 1): void
      * <?php
      * $email = $I->grabLastSentEmail();
      * $address = $email->getTo()[0];
-     * $I->assertSame('john_doe@user.com', $address->getAddress());
+     * $I->assertSame('john_doe@example.com', $address->getAddress());
      * ```
      *
      * @return \Symfony\Component\Mime\Email|null
@@ -72,8 +72,6 @@ public function grabLastSentEmail(): ?Email
      * ```php
      * <?php
      * $emails = $I->grabSentEmails();
-     * $address = $emails[0]->getTo()[0];
-     * $I->assertSame('john_doe@user.com', $address->getAddress());
      * ```
      *
      * @return \Symfony\Component\Mime\Email[]