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

tv42/old-go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme