Add a cron job to all Travis CI repos using the Travis CI API
Since you can only have 1 cronjob per branch per repo, this overwrites any existing crons
Args:
branch - defaults to 'master'
interval - defaults to 'monthly'. Options: daily, weekly, monthly
recent_dont_rerun - boolean, defaults to 'true'. Don't run cron job if a build has occurred in the last 24 hours. Set to 0 or 'false' to disable this, any other value is taken as 'true'