Bump rubygems version for Windows

There is a bug in ruby gems < 2.4.2 where the batch file created assumes ruby is in the same directory as it. This is not the case in rubygems >= 2.4.2, see https://github.com/rubygems/rubygems/pull/942
This causes problems when we `chef gem install foo`. Any binaries `foo` contains will have unusable batch files. See https://github.com/opscode/chef-dk/issues/239.

cc @btm @opscode/client-engineers