Support powershell in constrained mode

[ocalvo]

In highly secure environments, powershell can be configured to run in constrained mode.
In this mode, the dot evaluator is not permitted to run.

Description

This change uses Invoke-Expression to achieve the same behavior as before but allows for the module to work correctly in PowerShell constrained mode.

Related Issue

#138

Motivation and Context

Fix issue to allow the module to work correctly.

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.