devapp: change refresh to 5 minutes
devapp: change refresh to 5 minutes

The old dashboard on swtch.com refreshed every 5 minutes.
Surely we can do the same.
30 minutes is just too slow.

Change-Id: I338b3ae3277752e05bb2c7af42ba9770b8da6669
Reviewed-on: https://go-review.googlesource.com/23370
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

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