use " for nested double quote

[kejxu]

using ' (single quote) leads to the following error message on Windows:

>roslaunch kobuki_gazebo kobuki_empty_world.launch --screen
... logging to C:\Users\kejxu\.ros\log\fd82fbee-9a03-11e9-a567-480fcf49b453\roslaunch-kejxu-z240-882276.log
Checking log directory for disk usage. This may take a while.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.
[93mxacro: in-order processing became default in ROS Melodic. You can drop the option.[0m
[91minvalid mode ('r') or filename: 'C:\ros\catkin_ws\turtlebot2\install_isolated\share\kobuki_description\urdf\kobuki_standalone.urdf.xacro'[0m
[31mRLException: while processing C:\ros\catkin_ws\turtlebot2\install_isolated\share\kobuki_gazebo\launch\includes\robot.launch.xml:
Invalid <param> tag: Cannot load command parameter [robot_description]: command [C:/opt/ros/melodic/x64\lib\xacro\xacro.exe --inorder 'C:\ros\catkin_ws\turtlebot2\install_isolated\share\kobuki_description\urdf\kobuki_standalone.urdf.xacro'] returned with code [2].

Param xml is <param command="$(find xacro)/xacro --inorder '$(find kobuki_description)/urdf/kobuki_standalone.urdf.xacro'" name="robot_description"/>[0m
[31mThe traceback for the exception was written to the log file[0m

single quotation marks do not work well on Windows. for example, the following would not work:

cd 'nested_dir'

and this works:

cd "nested_dir"

suggesting to change to use "

reference: https://stackoverflow.com/questions/22468479/are-nested-double-quotes-incorrect-in-xml