puppetlabs-puppet_agent : install_powershell task fails on targets with older versions of powershell

Basic Info
Module Version: 3.0.0

Describe your issue in as much detail as possible...

The install_powershell task was recently updated to use the version_powershell task to detect if the puppet-agent packages was installed or not. The task uses the $PSScriptRoot variable to get the directory of the version_install script and then uses the ConvertFrom-Json cmdlet to parse the tasks output. This variable and cmdlet are not available in older versions of powershell (< 3.0), causing the task to fail on targets that have older versions of powershell installed.