[circle] Add check of external urls only when master
[circle] Add check of external urls only when master

dpshelio/openastronomy.github.io,Cadair/openastronomy.github.io,OpenAstronomy/openastronomy.github.io,OpenAstronomy/openastronomy.github.io,dpshelio/openastronomy.github.io,OpenAstronomy/openastronomy.github.io,dpshelio/openastronomy.github.io,Cadair/openastronomy.github.io,Cadair/openastronomy.github.io