notification: update failure mail

src/mail_templates/box_update_error-text.ejs

@@ -0,0 +1,17 @@
+Dear Cloudron Admin,
+
+Cloudron update failed because of the following reason:
+
+-------------------------------------
+
+<%- message %>
+
+-------------------------------------
+
+
+Powered by https://cloudron.io
+
+Don't want such mails? Change your notification preferences at <%= notificationsUrl %>
+
+Sent at: <%= new Date().toUTCString() %>
+