collate/build: documentation fix Fixes golang/go#19626. Change-Id: I5801d18b435ff115a2cf3ae5b21a4917afbe4625 Reviewed-on: https://go-review.googlesource.com/44378 Run-TryBot: Marcel van Lohuizen <mpvl@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>