Always add an extra newline to cron lines

Some users do edit cron files and save them without the trailing
newline. Such cron files are not valid, by adding the extra newline
before pushing them to kafka, we will not experience issues with things
mysteriously not running due to missing newlines.
Merge pull request #26 from Tarrasch/fix-trailing-newline-in-cron

Always add an extra newline to cron lines