This commit fixes the following warning in the puppet master's logs:
Jan 26 16:09:26 <daemon.warn> marvin puppet-master[68168]: The argument signature (String format, [String timezone]) is deprecated for #strfime. See #strftime documentation and Timespan type for more info
Jan 26 16:09:26 <daemon.warn> marvin puppet-master[68168]: (at /usr/local/etc/puppet/environments/production/modules/apt/manifests/update.pp:17)