CL (change list) pops out of nowhere and confuses the
reader. Use "change" instead to be consistent with the
rest of the document.

Fixes #18989.

Change-Id: I525a63a195dc6bb992c8ad0f10c2f2e1b2b952df
Reviewed-on: https://go-review.googlesource.com/36564Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>