Issues related to plot_histograms function

[AraiYuno]

Here is a git issue to keep track of all the issues and improvements for plot_histograms function.

[AraiYuno]

@harryyikhchan Based on your error messages, I diagnosed there is an error that I did not realize during initial testing.

I have made the fixes and confirmed that all the unit tests still pass. I have also confirmed that plot_histograms function runs fine on a jupyter notebook.

[harryyikhchan]

Thanks Kyle!