Remove download.ps1 and replace Powershell command with a one-liner.

Author: aholmes

build.cmd

@@ -5,7 +5,7 @@ if not exist .paket mkdir .paket
 
 if not exist .paket/paket.bootstrapper.exe (
   @echo "Installing Paket"
-  Powershell.exe -File download.ps1
+  Powershell.exe -Command "Invoke-WebRequest -Uri https://github.com/fsprojects/Paket/releases/download/2.12.5/paket.bootstrapper.exe -OutFile .paket\paket.bootstrapper.exe"
 
 
   .paket\paket.bootstrapper.exe prerelease