package.xml: use uppercase ROS_VERSION for buildtool_depend condition

* otherwise it won't be parsed correctly by superflore as explained in:
  "bitbake: use own condition_context instead of whole os.environ"
  commit from:
  ros-infrastructure/superflore#280

Signed-off-by: Martin Jansa <martin.jansa@lge.com>

package.xml

@@ -9,8 +9,8 @@
   <license>BSD</license>
   <author email="david.uhm@lge.com">David Uhm</author>
 
-  <buildtool_depend condition="$ros_version == 1">catkin</buildtool_depend>
-  <buildtool_depend condition="$ros_version == 2">ament_cmake</buildtool_depend>
+  <buildtool_depend condition="$ROS_VERSION == 1">catkin</buildtool_depend>
+  <buildtool_depend condition="$ROS_VERSION == 2">ament_cmake</buildtool_depend>
 
   <build_depend condition="$ROS_VERSION == 1">message_generation</build_depend>
   <build_depend condition="$ROS_VERSION == 2">rosidl_default_generators</build_depend>