Remove optional group fields
Remove optional group fields

On some platforms, change, uclass and expire are not supported, see
http://ruby-doc.org/stdlib-2.2.0/libdoc/etc/rdoc/Etc.html#Passwd for
details.

The gecos field is optional as well, but seems to be supported on most
mainstream Ruby versions, ie. those built by RVM and ruby-build as well
as the Rubies provided by all tested GNU/Linux distributions, OS X,
OpenBSD, ...

sometimesfood/fakeetc