[Jekyll] cannot load Jekyll-include-cache

When I run Jekyll in terminal, with

$ bundle exec jekyll serve &

I got Error message below

$ Dependency Error: Yikes! It looks like you don't have jekyll-include-cache or one of its dependencies 
installed. In order to use Jekyll as currently configured, you'll need to install this gem. The full error 
message from Ruby is: 'cannot load such file -- jekyll-include-cache' If you run into trouble, you can 
find helpful resources at https://jekyllrb.com/help/!

To solve this error, First I added gem 'jekyll-include-cache' Gemfile in root project path

$ vi Gemfile

source 'https://rubygems.org'
gem 'github-pages', group: :jekyll_plugins
gem 'jekyll-include-cache'

Still, another Error happened

$ Could not find gem 'jekyll-include-cache' in any of the gem sources listed in your Gemfile.

So, installed jekyll-include-cache

$ sudo gem install jekyll-include-cache

and then, I could build and run server