gopher: fix URL to Google merchandise store

Thanks to benjamin-rood for pointing it out.

Change-Id: I4bfcfe1bc4f9604a91c4181d078a23ca68b2cf5e
Reviewed-on: https://go-review.googlesource.com/18020
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Chris Broadfoot <cbro@golang.org>
1 file changed