Pin json_pure for ruby 1.9
Pin json_pure for ruby 1.9

Without this change, building on ruby 1.9 complains about the latest
version of json_pure requiring Ruby 2.x.  Here we pin the version of
json_pure in the case where RUBY_VERSION is set to 1.9.3.  This should
allow us to build on both 1.9 and 2.x.

zleswomp/puppetlabs-aws,daveseff/puppetlabs-aws,daveseff/puppetlabs-aws,gregohardy/puppetlabs-aws,hundredacres/puppetlabs-aws,DavidS/puppetlabs-aws,DavidS/puppetlabs-aws,benpillet/puppetlabs-aws,puppetlabs/puppetlabs-aws,gregohardy/puppetlabs-aws,zvymazal/puppetlabs-aws,puppetlabs/puppetlabs-aws,benpillet/puppetlabs-aws,marksyme/puppetlabs-aws,marksyme/puppetlabs-aws,zleswomp/puppetlabs-aws,zvymazal/puppetlabs-aws,hundredacres/puppetlabs-aws