go-tour/content/welcome.article: update restrictions of the playground.
go-tour/content/welcome.article: update restrictions of the playground.

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/182390043

raindev/tour,zorion/go-tour-ca,scryner/tour,LaPingvino/go-tour-eo,golians/tour,shuLhan/go-tour-id,Go-zh/tour,scryner/tour,dupoxy/go-tour-fr,LaPingvino/go-tour-eo,LaPingvino/go-tour-nl,ybin/tour,rofrol/go-tour-pl,bbandaru/tour,shuLhan/go-tour-id,shuLhan/go-tour-id,raindev/tour,ybin/tour,campoy/go-tour-ua,scryner/tour,LaPingvino/go-tour-nl,golians/tour,phoorichet/tour,tamnd/tour,campoy/go-tour-ua,LaPingvino/go-tour-eo,tamnd/tour,golians/tour,Go-zh/tour,Jasperste/tour,bbandaru/tour,shuLhan/tour,raindev/tour,Jasperste/tour,dupoxy/go-tour-fr,phoorichet/tour,rofrol/go-tour-pl,ybin/tour,phoorichet/tour,tamnd/tour,Go-zh/tour,LaPingvino/go-tour-nl,Jasperste/tour,bbandaru/tour,dupoxy/go-tour-fr,Go-zh/tour,shuLhan/tour,campoy/go-tour-ua,shuLhan/tour,zorion/go-tour-ca,rofrol/go-tour-pl,golang/tour,scryner/tour