spec: remove evaluation order inconsistency
spec: remove evaluation order inconsistency

This is a clarification of what happens already.
Not a language change.

Fixes issue 7137.

LGTM=iant, r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://codereview.appspot.com/96000044

wesolows/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang,wesolows/golang-old