Repair Shippable

[stevenschwenke]

Change https://github.com/stevenschwenke/JavaFXWorkshop/blob/master/shippable.yml according to Shippable/support#1447 to avoid

build_ci 0s
apt-get update 0s
E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied)
E: Unable to lock directory /var/lib/apt/lists/
E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied)
E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?