title: unable to start grunt - "TypeError: grunt.registerHelper is not a function" on ubuntu 16
body: <p>Unable to start grunt </p>
  
  <p>Trying to run <code>grunt serve</code> on a mean project but instead getting this:</p>
  
  <p><code>
  Running "serve" task
  Loading "clean.js" tasks...ERROR</p>
  
  <blockquote>
    <blockquote>
      <p>TypeError: grunt.registerHelper is not a function</p>
    </blockquote>
  </blockquote>
  
  <p>Running "clean:server" (clean) task
  Warning: grunt.helper is not a function Use --force to continue.</p>
  
  <p>Aborted due to warnings.</p>
  
  <p>Execution Time (2017-11-05 07:32:02 UTC+1)
  loading tasks        814ms  ▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇ 90%
  serve                 63ms  ▇▇▇ 7%
  loading grunt-clean   14ms  ▇ 2%
  Total 900ms
  </code></p>
  
  <p>any thoughts</p>