Prompt user to authorize when the access token is invalid

[raws]

When the cached access token is invalid for whatever reason (the user revoked access to the app, for example), we get a response like this:

{"data"=>{"error"=>"The access token provided is invalid.", "request"=>"/3/image.json", "method"=>"POST"}, "success"=>false, "status"=>403}

The script should prompt the user to re-authorize the app if they so desire.