Remove apostrophes in comments to workaround ros2/launch_ros#214

[oKermorgant]

Hi,

As seen in ros2/launch_ros#214 and ros2/launch_ros/issues/136 launch files may have trouble getting the output of a xacro command if the parsed xacro files contain special YAML characters (typically apostrophes / colons inside comments).

The launch file examples of Plankton use the OpaqueFunction approach that explicitly runs xacro to generate a temporary URDF file. On the other hand, if the Command substitution is used (which is a common practice) then it fails on the current xacro files from Plankton.

This PR simply removes the apostrophes in the comments, following the same workaround as other people did.

[jpliquid]

Hi @oKermorgant,

I didn't know about apostrophes, but indeed I had noticed parsing errors due to colons inside comments (thank you for the related issues), which prevented me from using the Command substitution as you pointed out. Thanks for your contribution.