killbill_helper: remove ruby-2.0 double star operator

Don't force 1.9 users to upgrade.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
killbill_helper: add missing audit arguments in API calls

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
account_timelines: is_fully_refunded? is not defined in killbill-client

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
gemspec: update killbill-client-ruby to 0.2.1

Fix authentication in refresh calls.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>