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

pombredanne/go-deleteme,tv42/old-go,tv42/old-go,dsriram/golang,dsriram/golang,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,gnanderson/go,tv42/old-go,gnanderson/go,dsriram/golang,pombredanne/go-deleteme,dsriram/golang,dsriram/golang,apparentlymart/golang,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,gnanderson/go,pombredanne/go-deleteme,apparentlymart/golang,dsriram/golang,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,dsriram/golang,tv42/old-go,apparentlymart/golang,gnanderson/go