Switch back to require_relative

[danielparks]

@danielparks Hi!
thanks for the awesomme module. Stupid question, could you revert this commit? With require_relative, environment isolation works. Puppet will ensure that the loaded lib comes from the same environment as the type and provider. With just using require, you potentially load the puppet_x lib from another code environment and cause some trouble. An example PR is puppetlabs/puppetlabs-stdlib#1275. We (voxpupuli.org) and Puppet are currently checking for a rubocop rule to even enforce require_relative.

Originally posted by @bastelfreak in #29 (comment)