title: Auto-generate class is not updating with build_runner
body: <p>I am using a <strong>build_runner</strong> to generate auto-generated code in the flutter project.</p>
  
  <p>Issue: When I make an update in the model class and then I try to run below command, but it does not update auto-generated class.</p>
  
  <p>Command: </p>
  
  <pre><code>pub run build_runner build
  </code></pre>
  
  <p>Dart Packages:</p>
  
  <pre><code>built_value: '&gt;=5.5.5 &lt;7.0.0'
  
  build_runner: ^1.5.0
  
  built_value_generator: ^6.6.0
  </code></pre>
  
  <p>After the execution of the command for <strong>build_runner</strong>, an auto-generated class should be updated.</p>