commit 28b4e3e4be86ec508df6d4c354752b2a267e4d2c
Author: Hunter L. Allen <hallen@kns.com>
Date: Mon Dec 10 11:51:07 2018 -0500

Add gazebo 9 (#720)

* Use newer sdformat for gazebo 9

* Use ignition-math6 for newest sdformat

* Move ignition msgs to match other ignition package category

* Fix ignition-transport double install

* Add tinyxml2 version 7

* Add patches for gazebo 9.4.1