env/windows: update winstrap version
env/windows: update winstrap version

Change-Id: Ifd9cdd5ec202dbfcf985cbdee598a636b38e5a37
Reviewed-on: https://go-review.googlesource.com/4521
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

evandbrown/build,evandbrown/build,golang/build,proppy/build,golang/build,evandbrown/build,golang/build,proppy/build,proppy/build,proppy/build,golang/build