workaround missing librarian-puppet dependencies

librarian-puppet-maestrodev gem specifies Ruby 1.8 dependencies incorrectly. open3_backport and json are required on Ruby 1.8
but are not currently installed. See
https://github.com/maestrodev/librarian-puppet/issues/16
Merge pull request #237 from 3flex/patch-1

workaround missing librarian-puppet-maestrodev dependencies