/usr/local/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require': cannot load such file -- sequel (LoadError)
    from /usr/local/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
    from dna_in.rb:2:in `<main>'

 使用 bundle install 安装的 gem, 在代码中 require, 运行时如果提示 cannot load such file, 使用 bundle exec 执行即可