Add missing require ffi_yajl in System class
Add missing require ffi_yajl in System class

This is used several times in this class, but not required.

Signed-off-by: Tim Smith <764ef62106582a09ed09dfa0b6bff7c05fd7d1e4@chef.io>

jaymzh/ohai,chef/ohai,chef/ohai,mattray/ohai,mattray/ohai,higanworks/ohai,jaymzh/ohai,higanworks/ohai