doc: simplify a go1.3 change description
doc: simplify a go1.3 change description

LGTM=r
R=rsc, r
CC=golang-codereviews
https://codereview.appspot.com/87750043

apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang