cmd/tip: enable playground on tip.golang.org

Updates golang/go#28536

Change-Id: I3ece72aacd4635f4580be404672394a47791a1e8
Reviewed-on: https://go-review.googlesource.com/c/146917
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed
tree: fd725bb4c3111462f1aa282f83e7bf0876a9f7bf
  1. cmd/