collate/build: fix go vet warning about Fprintln
collate/build: fix go vet warning about Fprintln

  builder.go:505: Fprintln call ends with newline

LGTM=mpvl, josharian
R=golang-codereviews, josharian, mpvl
CC=golang-codereviews
https://codereview.appspot.com/108260043

Committer: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>

bryanxu/go-zh.text,webfd/go-zh.text,d0f/go-zh.text,scalingdata/go.text,ssor/normGo