title: fs-extra copy file outputs blank file
body: <p>When I run the following code a blank file gets created with the correct name. I clearly dont want a blank file.</p>
  
  <p>I know the path is correct because when i make it purposely incorrect it fails (obviously)</p>
  
  <pre><code>const path = require('path');
  const fse = require('fs-extra');
  const OUTPUT_PATH   = 'js/libs/';
  const _NODE_MODULES   = 'node_modules/';
  const filePath        = `${_NODE_MODULES}tooltipster/dist/js/tooltipster.bundle.min.js`;
  
  fse.copy(path.join(__dirname, filePath), path.join(__dirname, `${OUTPUT_PATH}/something.js`), err =&gt; {
    if (err) {
      console.log(err);
      process.exit(1)
    }
    console.log('Copy complete');
    process.exit(0);
  })
  </code></pre>
  
  <p>Output of this is
  <code>Copy Complete</code> 
  But the file is blank as I previously stated. Any idea what I'm doing wrong here?</p>