dashboard: increase TIMEOUT_SCALE to 2 for windows-amd64
dashboard: increase TIMEOUT_SCALE to 2 for windows-amd64

cmd/go takes ~188 seconds on windows-amd64, which is over the
default 180 second limit. Bump up the timout rate.

Change-Id: Ib0e5289ab6c4d6127d18375e3a72453818b984a8
Reviewed-on: https://go-review.googlesource.com/110415
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build