(GH-981) Add option to use Get-FileHash for versions v4.x and above

For compatibility reasons, Chocolatey suggests using `choco install
checksum` to verify checksums.

But, in Powershell v4 and beyond, users could choose to run
`Get-FileHash` as well.

This change adds a message in applicable powershell versions (v4.x and
later) to suggest this course of action.

src/chocolatey.resources/helpers/functions/Get-CheckSumValid.ps1

@@ -146,6 +146,9 @@ param(
 
     Write-Warning "Missing package checksums are not allowed (by default for HTTP/FTP, `n HTTPS when feature 'allowEmptyChecksumsSecure' is disabled) for `n safety and security reasons. Although we strongly advise against it, `n if you need this functionality, please set the feature `n 'allowEmptyChecksums' ('choco feature enable -n `n allowEmptyChecksums') `n or pass in the option '--allow-empty-checksums'. You can also pass `n checksums at runtime (recommended). See `choco install -?` for details."
     Write-Debug "If you are a maintainer attempting to determine the checksum for packaging purposes, please run `n 'choco install checksum' and run 'checksum -t sha256 -f $file' `n Ensure you do this for all remote resources."
+    if ($PSVersionTable.PSVersion.Major -ge 4){ 
+      Write-Debug "Because you are running Powershell with a major version of v4 or greater, you could also opt to run `n '(Get-FileHash -Path $file -Algorithm SHA256).Hash' `n rather than install a separate tool."
+    }
 
     if ($env:ChocolateyPowerShellHost -eq 'true') {
       $statement = "The integrity of the file '$([System.IO.Path]::GetFileName($file))'"