This change adds the scopes rclone wants during the oauth request.
Previously rclone left these blank to get a default set.
This allows rclone to add the "members.read" scope which is necessary
for "impersonate" to work, but only when it is in use as it require
authorisation from a Team Admin.
See: https://forum.rclone.org/t/dropbox-no-members-read/22223/3
37e630178e