plot_pathline with wrong color argument in Modpath Notebooks

[javgs-bd]

This is a minor thing but just noticed that in the current modpath flopy notebooks there are several calls to plot_pathline with a "color" argument that result in grey lines.

Reviewing the docs and other calls that work I believe the argument is "colors" instead.

[wpbonelli]

Thanks @javgs-bd you are right. @langevin-usgs I could add this fix to #1687, or would it be best as a separate PR?

[christianlangevin]

I'd so go ahead and add it to #1687, and then let's merge it in.

[wpbonelli]

closed by #1687