Ruby 1.9.3 and json_pure 2.0.2

Hiera has a dependency on json_pure of >= 0: https://github.com/puppetlabs/hiera/blob/master/.gemspec

json_pure 2.0.2 dropped support for Ruby 1.9.3, so installs of Hiera, and therefore also Puppet, now fail on environments with Ruby 1.9.3.

Something needs to be added that restricts the version of json_pure to <= 2.0.1 if ruby is 1.9.3. I believe Kylo has mentioned to me in a PR that there are no plans to up the minimum ruby requirement for Puppet prior to 5.0, so I think this is the path of least resistance here.