Set noreply@HOSTNAME for reply_to field in all emails

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/mailers/notify.rb

@@ -16,6 +16,7 @@ class Notify < ActionMailer::Base
   default_url_options[:script_name] = Gitlab.config.gitlab.relative_url_root
   default from: Gitlab.config.gitlab.email_from
+  default reply_to: "noreply@#{Gitlab.config.gitlab.host}"
   # Just send email with 3 seconds delay
   def self.delay