update ffi gem
update ffi gem

Appease CVE check that finds CVE-2018-1000201:

> ruby-ffi version 1.9.23 and earlier has a DLL loading issue which can
> be hijacked on Windows OS

Supermarket does not run on Windows, so it is not affected by this CVE.
This change is to help reduce the noise of CVE audits.

Signed-off-by: Robb Kidd <11cd4f9ba93acb67080ee4dad8d03929f9e64bf2@chef.io>

chef/supermarket,robbkidd/supermarket,chef/supermarket,robbkidd/supermarket,chef/supermarket,robbkidd/supermarket,robbkidd/supermarket,chef/supermarket,chef/supermarket