xacro now requires some parameters in order

[M1chaelM]

• Our wayfinding.yaml file generates a wayfinding.world.xacro that calls the wayfinding.xacro when xacro is run on it to create a wayfinding.world.
• The first two parameters of the wayfinding.xacro are **wp_markers and **waypoints.
• Previously, our yaml listed the **waypoints parameter before the **wp_markers parameter, and this generated a xacro in which the <waypoints> element appeared before the <wp_markers> element, but xacro still correctly matched the arguments and inserted them in the right place.
• Now it seems that the blocks to be inserted are just taken in the order they appear, so listing <waypoints> first causes it to be treated as the argument to **wp_markers.

I'm guessing this is a change to xacro but I'm not entirely sure.