Disable autoescaping for plain text email

src/Packagist/WebBundle/Resources/views/Email/update_failed.txt.twig

@@ -1,3 +1,4 @@
+{% autoescape false -%}
 > Disclaimer: These email notifications are in experimental stage, if you find
 > that they look strange or contain false or misleading information please
 > reply to this email to let us know.
@@ -19,3 +20,4 @@ Below is the full update log which should highlight errors as
 --
 If you do not wish to receive such emails in the future you can disable
 notifications on your profile page: https://packagist.org/profile/edit
+{%- endautoescape %}