mistake in phonon dispersion example?

[alpinnovianus]

Dear Pranab das,

in your plotting code for the phonon dispersion example,
https://pranabdas.github.io/espresso/hands-on/phonon

is there a mistake in the area I highlighted with red circle? why is there a slanted line slightly above the x-axis?
i don't think the line should be there...
if it is a mistake, could you please inform how to fix the plotting code?

thank you.
alpin