dashboard: make git dashboard the default

Also bump the watcher version, so the old watcher doesn't try to write
to the new dashboard.

Change-Id: I7f62ad937fe162dadfd1222f56a3c5e493be9a61
Reviewed-on: https://go-review.googlesource.com/1357
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>