Checking that the variable OSRelease::ID_LIKE is defined before using it.

In the line 517 of the file neondocker.rb the variable OSRelease::ID_LIKE is being used to check if the OS is Ubuntu and then do something specific. The problem is that some distributions don't define this in the os-release file, which causes a failure while trying to execute this script.

We can see some examples in this Gist: Distribution Detection For example, my distribution is Archlinux, which doesn't define the variable.