title: How to put captured regex group to OutputFilePath?
body: <p>is there anyway to put the captured regex group from outputFilePath value to outputFilePath in JoinTo Javascript?</p>
  
  <p>In my brunch-config.js</p>
  
  <pre><code>javascripts: {
      joinTo: {
          '${1}.js': /app\/(\w+)\//
      }
    },
  </code></pre>
  
  <p>So if i have a sub folder name 'beta1', all the Js files in that folder will be merged to beta1.js (the sub-folder name)</p>
  
  <p>But now, all js files in subfolders are in $1.js file.</p>
  
  <p>Im using Brunch: 2.8.0 with Node: 4.4.3 and NPM: 2.15.1. Thank you.</p>