title: Rails 5.2.0.rc1 + Webpacker 3.3.0 Unable to find dev_server configuration
body: <p>Using Docker and Docker Compose, I'm unable to get the webpacker service up and running after upgrading to webpacker 3.3.0. The output after <code>docker-compose up</code> is:</p>
  
  <pre><code>webpack dev_server configuration not found in /app/config/webpacker.yml.
  Please run bundle exec rails webpacker:install to install Webpacker
  </code></pre>
  
  <p>I've run <code>webpacker:install</code> - it made changes but the output is the same. I've also run <code>rails new test --webpacker</code> and compared the configuration files. So far the only notable difference between the working generated app and my own is the Node version. On my local machine in a typical RVM environment the node version is <code>v9.4.0</code> and in the docker images it's <code>v8.9.3</code>. Yarn in both environments is <code>1.3.2</code>.</p>
  
  <p>My config/webpacker.yml is almost exactly the same as generated. The only difference is a few added extensions:</p>
  
  <pre><code># Note: You must restart bin/webpack-dev-server for changes to take effect
  
  default: &amp;default
    source_path: app/javascript
    source_entry_path: packs
    public_output_path: packs
    cache_path: tmp/cache/webpacker
  
    # Additional paths webpack should lookup modules
    # ['app/assets', 'engine/foo/app/assets']
    resolved_paths: []
  
    # Reload manifest.json on all requests so we reload latest compiled packs
    cache_manifest: false
  
    extensions:
      - .coffee
      - .erb
      - .js
      - .jsx
      - .ts
      - .vue
      - .sass
      - .scss
      - .css
      - .module.sass
      - .module.scss
      - .module.css
      - .png
      - .svg
      - .gif
      - .jpeg
      - .jpg
  
  development:
    &lt;&lt;: *default
    compile: true
  
    # Reference: https://webpack.js.org/configuration/dev-server/
    dev_server:
      https: false
      host: localhost
      port: 3035
      public: localhost:3035
      hmr: false
      # Inline should be set to true if using HMR
      inline: true
      overlay: true
      compress: true
      disable_host_check: true
      use_local_ip: false
      quiet: false
      headers:
        'Access-Control-Allow-Origin': '*'
      watch_options:
        ignored: /node_modules/
  
  
  test:
    &lt;&lt;: *default
    compile: true
  
    # Compile test packs to a separate directory
    public_output_path: packs-test
  
  production:
    &lt;&lt;: *default
  
    # Production depends on precompilation of packs prior to booting for performance.
    compile: false
  
    # Cache manifest.json for performance
    cache_manifest: true
  </code></pre>
  
  <p>config/webpack/environment.js:</p>
  
  <pre><code>const { environment } = require('@rails/webpacker')
  
  module.exports = environment
  </code></pre>
  
  <p>config/webpack/development.js:</p>
  
  <pre><code>const environment = require('./environment')
  
  module.exports = environment.toWebpackConfig()
  </code></pre>
  
  <p>Any ideas as to why it's not finding the dev_server configuration? I don't believe the node version is the reason.</p>