plot_on_map.py issues

[ssantellanes]

Documentation states the following "Usage: python -OPTION plot_on_map.py output.arrivals.dat figure.png."
It should be "python plot_on_map.py -OPTION output.arrivals.dat figure.png."

In addition, raypaths_file in run() is leading to errors with the script. Fix implemented by me on my local version is to delete it from the args for run(), as it is not used in the script.