Now that maps are printed in deterministic order, the map example
can have multiple keys without breaking the build.

Change-Id: Iccec0cd76a3d41c75d8d4eb768ec0ac09ad9f2ad
Reviewed-on: https://go-review.googlesource.com/c/151218Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>