Invalid multiline cronjob validation

The cronjob validator considers folded blocks to be single line strings.  Due to the YAML specification adding a `\n` to the end of a folded block, this results in a cronjob that looks like this:

```
> cat /lagoon/crontabs/crontab 
* * * * * flock -n /tmp/cron.lock/xxxxxx 'command
'
```
