PS script uses .NET 4 features, so requires Powershell 3.0

The Powershell script code uses String.IsNullOrWhiteSpace. This method was introduced in .NET 4.0. PowerShell 3.0 is required to use .NET 4.0 features.
Merge pull request #16 from ringods/master

PS script uses .NET 4 features, so requires Powershell 3.0