doc/go_spec: fix broken link         Part of issue 3424
doc/go_spec: fix broken link
        Part of issue 3424

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/5955049

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang