Why can't I install the github-pages plug-in when I set up Jekyll?

Problem
The following issues occur while following the Step.8 of guide in the following section:

System Specifications

  • Ubuntu 19.10 x64
  • Ruby: ruby 2.5.5p157 (2019-03-15 revision 67260) [x86_64-linux-gnu]
  • Gem: 2.7.6.2
  • Bundler: 2.1.
  • Jekyll: 4.0.0

Reference

try bundle install and see if that works.

Thank you for your answer.

I tried that already. :sob: