fix powershell script for powershell no-config debug (microsoft#610)

Author: eleanorjboyd

bundled/scripts/noConfigScripts/debugpy.ps1

@@ -1,6 +1,7 @@
 # PowerShell script
-if ($PSVersionTable.OS -match "Windows") {
+$os = [System.Environment]::OSVersion.Platform
+if ($os -eq [System.PlatformID]::Win32NT) {
     python $env:BUNDLED_DEBUGPY_PATH --listen 0 --wait-for-client $args
 } else {
     python3 $env:BUNDLED_DEBUGPY_PATH --listen 0 --wait-for-client $args
-}
+}