title: How to exclude webpack from bundling .spec.js files
body: <p>my Package.bundle reads </p>
  
  <pre><code>var reqContext = require.context('./', true, /\.js$/);
  
  reqContext.keys().map(reqContext);
  </code></pre>
  
  <p>Which basically includes all .js files.</p>
  
  <p>I want the expression to exclude any ***.spec.js files . Any regexp here to exclude .spec.js files ?</p>