trying to install this - https://github.com/brandonfang/lilnotion/tree/ad36f85f9856af09e08478b71a8cefed936db0bc - that commit. ruby 2.5.1 w react

terminal.js

~/complete-notion$ bin/rails server
Warning: the running version of Bundler (2.1.2) is older than the version that created the lockfile (2.2.18). We suggest you to upgrade to the version that created the lockfile by running `gem install bundler:2.2.18`.
Could not find pg-1.2.3 in any of the sources
Run `bundle install` to install missing gems.

source: https://github.com/brandonfang/lilnotion/tree/ad36f85f9856af09e08478b71a8cefed936db0bc

im using rbenv:
~/complete-notion$ rbenv versions
* system (set by /home/students/.rbenv/version)
  2.5.1

If I use 2.5.1 instead? 
~/complete-notion$ rbenv global 2.5.1
~/complete-notion$ rbenv local 2.5.1
...
~/complete-notion$ bin/rails server
Traceback (most recent call last):
        4: from bin/rails:3:in `<main>'
        3: from bin/rails:3:in `load'
        2: from /home/students/complete-notion/bin/spring:8:in `<top (required)>'
        1: from /home/students/.rbenv/versions/2.5.1/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
/home/students/.rbenv/versions/2.5.1/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require': cannot load such file -- bundler (LoadError)

if ...
Edit: If I do a gemfile install first, then run rails server
~/complete-notion$ gem install gemfile
...
Done installing documentation for gemfile after 0 seconds
1 gem installed
...

~/complete-notion$ bin/rails server
Traceback (most recent call last):
        4: from bin/rails:3:in `<main>'
        3: from bin/rails:3:in `load'
        2: from /home/students/complete-notion/bin/spring:8:in `<top (required)>'
        1: from /home/students/.rbenv/versions/2.5.1/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
/home/students/.rbenv/versions/2.5.1/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require': cannot load such file -- bundler (LoadError)
~/complete-notion$ bundle install
Traceback (most recent call last):
        2: from /home/students/.rbenv/versions/2.5.1/bin/bundle:23:in `<main>'
        1: from /home/students/.rbenv/versions/2.5.1/lib/ruby/2.5.0/rubygems.rb:308:in `activate_bin_path'
/home/students/.rbenv/versions/2.5.1/lib/ruby/2.5.0/rubygems.rb:289:in `find_spec_for_exe': can't find gem bundler (>= 0.a) with executable bundle (Gem::GemNotFoundException)
~/complete-notion$
I pretty newbie to rails and ruby so i dont know whats happening
used to java, js, python, golang, c and those easy langs : ) 
i wrap it into athread
i wrap it into a gist