doc/go_spec: cap doesn't apply to maps Fixes issue 4682.
doc/go_spec: cap doesn't apply to maps
Fixes issue 4682.

R=golang-dev, adg, dave
CC=golang-dev
https://codereview.appspot.com/7094062

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