cmd/tip: bump verison serving tip.golang.org to HEAD

This picks up a recent change to the playground package.

Change-Id: I9b5f0ef9981373274d707014a2c0e2786e9624c0
Reviewed-on: https://go-review.googlesource.com/22538
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed