ignition-gazebo6 6.0.0 (#1613)
ignition-gazebo6 6.0.0 (#1613)

* ignition-gazebo6: update 6.0.0

* update  bottle.

Co-authored-by: Louise Poubel <a8a345be5c4ec9546d4a8b399c0256542c1e44a6@openrobotics.org>
osrf/homebrew-simulation,scpeters/homebrew-simulation