title: How fix the issue when used the acviteadmin gem?
body: <p><img src="https://i.stack.imgur.com/XuwNJ.png" alt="enter image description here">Use the activeadmin into the gem file. <code>bundle install</code>, <code>rails g active_admin:install User</code>, then <code>rails s</code>, the server will crash and give some warning.</p>
  
  <p>Error Information:</p>
  
  <blockquote>
    <p><code>rails s</code></p>
  
  <pre><code>WARNING: Nokogiri was built against LibXML version 2.9.4, but has dynamically loaded 2.8.0
  =&gt; Booting WEBrick
  =&gt; Rails 5.0.0 application starting in development on http://localhost:3000
  =&gt; Run `rails server -h` for more startup options
  DEPRECATION WARNING: You are using the a deprecated processor interface #&lt;Proc:0x0055902480b218@/home/guo/.rvm/gems/ruby-2.3.1/gems/autoprefixer-rails-5.2.1.3/lib/autoprefixer-rails/sprockets.rb:25&gt;.
  Please update your processor interface:
  https://github.com/rails/sprockets/blob/master/guides/extending_sprockets.md#supporting-all-versions-of-sprockets-in-processors
   (called from install at /home/guo/.rvm/gems/ruby-2.3.1/gems/autoprefixer-rails-5.2.1.3/lib/autoprefixer-rails/sprockets.rb:25)
  Exiting
  </code></pre>
  </blockquote>
  
  <p>Here is my gem list.</p>
  
  <pre><code>source 'https://rubygems.org'
  
  # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
  gem 'rails', '5.0.0'
  
  # Use postgresql as the database for Active Record
  gem 'pg', '~&gt; 0.15'
  
  # Use SCSS for stylesheets
  gem 'sass-rails', '~&gt; 5.0'
  
  # Use Uglifier as compressor for JavaScript assets
  gem 'uglifier', '&gt;= 1.3.0'
  
  # Use CoffeeScript for .coffee assets and views
  gem 'coffee-rails', '~&gt; 4.1.0'
  
  # See https://github.com/rails/execjs#readme for more supported runtimes
  gem 'therubyracer', platforms: :ruby
  # Use jquery as the JavaScript library
  gem 'jquery-rails'
  
  # Turbolinks makes following links in your web application faster.
  # Read more: https://github.com/rails/turbolinks
  gem 'turbolinks'
  
  # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
  gem 'jbuilder', '~&gt; 2.0'
  
  # bundle exec rake doc:rails generates the API under doc/api.
  gem 'sdoc', '~&gt; 0.4.0', group: :doc
  
  gem 'activeadmin'
  gem 'devise'
  gem 'cancancan'
  gem 'rolify'
  gem 'draper'
  gem 'pundit'
  
  # Use ActiveModel has_secure_password
  gem 'bcrypt', '~&gt; 3.1.7'
  
  gem 'bootstrap-sass', '~&gt;3.3.7'
  gem 'autoprefixer-rails', '~&gt;5.2.1'
  #gem "twitter-bootstrap-rails"
  
  gem 'carrierwave', '&gt;= 1.0.0.beta', '&lt; 2.0' gem 'rmagick'
  
  gem 'grape'
  
  gem 'doorkeeper'
  
  gem "rack-oauth2"
  
  #gem 'will_paginate', '~&gt; 3.1.1' gem 'kaminari'
  
  gem 'dalli' gem 'actionpack-page_caching' gem 'actionpack-action_caching'
  
  gem 'delayed_job' gem 'delayed_job_active_record' #gem "sidekiq"
  
  #gem "devise-doorkeeper"
  
  gem 'roadie'
  gem 'roadie-rails'
  gem 'nokogiri', '1.6.0'
  #gem 'premailer-rails'
  </code></pre>