Copy-and-paste bug was putting scripts in the categories map.

Fixes #18186.

Change-Id: Ife9d9bdd346fe24e578dbb2a0aac7ef6e889ae68
Reviewed-on: https://go-review.googlesource.com/45830
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>