jekyll serve 报错/usr/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load

执行jekyll serve具体报错信息如下：

/usr/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- bundler (LoadError)
    from /usr/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /home/sky/.gem/ruby/2.4.0/gems/jekyll-3.5.1/lib/jekyll/plugin_manager.rb:46:in `require_from_bundler'
    from /home/sky/.gem/ruby/2.4.0/gems/jekyll-3.5.1/exe/jekyll:9:in `<top (required)>'
    from /home/sky/.gem/ruby/2.4.0/bin/jekyll:22:in `load'
    from /home/sky/.gem/ruby/2.4.0/bin/jekyll:22:in `<main>'

原因未安装bundler
解决方法：$ gem install bundler