spec: add dropped comma The proposed text in the last CL had a comma that was missing from the submitted spec.
spec: add dropped comma
The proposed text in the last CL had a comma that was missing from the submitted spec.

LGTM=gri
R=gri
CC=golang-codereviews
https://codereview.appspot.com/150720043

tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go