Update install_sysprep.ps1
Update install_sysprep.ps1

Fixing the meaning of "Head" in the install_sysprep script.
ning-yang/compute-image-windows,GoogleCloudPlatform/compute-image-windows,ning-yang/compute-image-windows,adjackura/compute-image-windows,illfelder/compute-image-windows,adjackura/compute-image-windows,Derekolds/compute-image-windows,GoogleCloudPlatform/compute-image-windows,illfelder/compute-image-windows