package.xml: Minor clean-up

Author: wxmerkt

package.xml

@@ -13,8 +13,10 @@
 
   <build_depend>git</build_depend>
   <build_depend>doxygen</build_depend>
-  <!-- The following tags are recommended by REP-136 -->
+
+  <!-- The following tag is recommended by REP-136 -->
   <exec_depend condition="$ROS_VERSION == 1">catkin</exec_depend>
+
   <depend condition="$ROS_PYTHON_VERSION == 2">python</depend>
   <depend condition="$ROS_PYTHON_VERSION == 3">python3</depend>
   <depend condition="$ROS_PYTHON_VERSION == 2">python-numpy</depend>