[release-branch.go1.3] go/build: update doc.go for go1.3 build tag.

««« CL 102470045 / f15ad332ce13
go/build: update doc.go for go1.3 build tag.

LGTM=bradfitz
R=adg, rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/102470045

»»»

LGTM=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/105310044
1 file changed