ur_gazebo: escape underscore in changelog. Fix #279.

ur_gazebo/CHANGELOG.rst

@@ -27,7 +27,7 @@ Changelog for package ur_gazebo
 * Added definitions for adding tergets in install folder. Issue `#10 <https://github.com/ros-industrial/universal_robot/issues/10>`_.
 * Added definitions for adding tergets in install folder. Issue `#10 <https://github.com/ros-industrial/universal_robot/issues/10>`_.
 * Updated to catkin.  ur_driver's files were added to nested Python directory for including in other packages.
-* removed arm_ prefix from joint names in gazebo controller config
+* removed ``arm_`` prefix from joint names in gazebo controller config
 * Renamed packages and new groovy version
 * Added ur10 and renamed packages
 * Contributors: IPR-SR2, Kelsey, Mathias Lüdtke, ipa-nhg, robot