This is not a problem. Information for people using Googlecolab.
How to use IRuby on Google Colab.
https://dev.to/kojix2/ruby-kernel-in-google-colaboratory-32ni
If Daru::View.plotting_library and Daru::View::Plot are in the same cell, it works well.

But when Daru::View.plotting_library and Daru::View::Plot are in the different cells, it does not show anything.
