Masalah :
Setelah melakukan perintah “bundle update” jekyll tidak bisa dijalankan dan muncul error EventMachine seperti dibawah ini :

E:\data\github\nuzulul.github.io>bundle exec jekyll serve --future --livereload

Configuration file: E:/data/github/nuzulul.github.io/_config.yml
            Source: E:/data/github/nuzulul.github.io
       Destination: E:/data/github/nuzulul.github.io/_site
 Incremental build: disabled. Enable with --incremental
      Generating...
       Jekyll Feed: Generating feed for posts
                    done in 1.441 seconds.
 Auto-regeneration: enabled for 'E:/data/github/nuzulul.github.io'
Unable to load the EventMachine C extension; To use the pure-ruby reactor, requi
re 'em/pure_ruby'
Traceback (most recent call last):
        22: from E:/portable/Ruby25/bin/jekyll:23:in `<main>'
        21: from E:/portable/Ruby25/bin/jekyll:23:in `load'
        20: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/jekyll-3.9.0/exe/je
kyll:15:in `<top (required)>'
        19: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/mercenary-0.3.6/lib
/mercenary.rb:19:in `program'
        18: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/mercenary-0.3.6/lib
/mercenary/program.rb:42:in `go'
        17: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/mercenary-0.3.6/lib
/mercenary/command.rb:220:in `execute'
        16: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/mercenary-0.3.6/lib
/mercenary/command.rb:220:in `each'
        15: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/mercenary-0.3.6/lib
/mercenary/command.rb:220:in `block in execute'
        14: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/jekyll-3.9.0/lib/je
kyll/commands/serve.rb:75:in `block (2 levels) in init_with_program'
        13: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/jekyll-3.9.0/lib/je
kyll/commands/serve.rb:93:in `start'
        12: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/jekyll-3.9.0/lib/je
kyll/commands/serve.rb:93:in `each'
        11: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/jekyll-3.9.0/lib/je
kyll/commands/serve.rb:93:in `block in start'
        10: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/jekyll-3.9.0/lib/je
kyll/commands/serve.rb:101:in `process'
         9: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/jekyll-3.9.0/lib/je
kyll/commands/serve.rb:147:in `register_reload_hooks'
         8: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/jekyll-3.9.0/lib/je
kyll/commands/serve.rb:147:in `require_relative'
         7: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/jekyll-3.9.0/lib/je
kyll/commands/serve/live_reload_reactor.rb:3:in `<top (required)>'
         6: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/jekyll-3.9.0/lib/je
kyll/commands/serve/live_reload_reactor.rb:3:in `require'
         5: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/em-websocket-0.5.2/
lib/em-websocket.rb:3:in `<top (required)>'
         4: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/em-websocket-0.5.2/
lib/em-websocket.rb:3:in `require'
         3: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/eventmachine-1.2.7-
x86-mingw32/lib/eventmachine.rb:8:in `<top (required)>'
         2: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/eventmachine-1.2.7-
x86-mingw32/lib/eventmachine.rb:8:in `require'
         1: from E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/eventmachine-1.2.7-
x86-mingw32/lib/rubyeventmachine.rb:2:in `<top (required)>'
E:/portable/Ruby25/lib/ruby/gems/2.5.0/gems/eventmachine-1.2.7-x86-mingw32/lib/r
ubyeventmachine.rb:2:in `require': cannot load such file -- 2.5/rubyeventmachine
 (LoadError)

Penyebab :
Setelah perintah “bundle update” ada 2 EventMachine di library

 1. eventmachine-1.2.7
 2. eventmachine-1.2.7-x86-mingw32

Solusi 1:

Unistall EventMachine yang no 2

E:\data\github\nuzulul.github.io>gem uninstall eventmachine

Select gem to uninstall:
 1. eventmachine-1.2.7
 2. eventmachine-1.2.7-x86-mingw32
 3. All versions
> 2
Successfully uninstalled eventmachine-1.2.7-x86-mingw32

Solusi 2 :

Tambahkan gem

gem 'eventmachine', '1.2.7', git: 'https://github.com/eventmachine/eventmachine', tag: 'v1.2.7'

Referensi :

https://github.com/eventmachine/eventmachine/issues/820