delete the correct shadow copies

Cleanup-SystemTempFiles.ps1

@@ -120,13 +120,13 @@ If ( Test-Path $ADSKInst ) {
 # Delete all but most recent shadow copy of system drive
 $SystemVolume = Get-CimInstance -ClassName Win32_Volume -ErrorAction SilentlyContinue | Where-Object { $_.Name -like "${Env:SystemDrive}\" }
 $ShadowCopies = Get-CimInstance -ClassName Win32_ShadowCopy | Where-Object { $_.VolumeName -like $SystemVolume.DeviceID }
-If ( $ShadowCopies.Length -gt 1 ) {
-    Write-Output "Deleting all of the oldest shadow copies on ${Env:SystemDrive}"
-    $ShadowsToDelete = $ShadowCopies.Length - 1
+If ( $ShadowCopies.Count -gt 1 ) {
+    Write-Output "Deleting all of the oldest shadow copies of ${Env:SystemDrive}"
+    $ShadowsToDelete = $ShadowCopies.Count - 1
     While ( $ShadowsToDelete -gt 0 ) {
-        $ShadowsToDelete = $ShadowsToDelete - 1
         vssadmin delete shadows /For=$Env:SystemDrive /Oldest /Quiet
-    }   
+        $ShadowsToDelete = $ShadowsToDelete - 1
+    }
 }
 
 # Delete old temp directories from Chocolatey cache