cmd/go has grown slow, even in short mode, and it's now regularly
failing on a number of builders where it's taking over the previous 3
minute timeout. for now, give it more time.
Change-Id: If565baf71c2770880b2e2139b47e03433951331f
Reviewed-on: https://go-review.googlesource.com/84235 Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>