title: Can you gulp clean all files in a directory except for a single file?
body: <p>Is there a way to use gulp-clean such that instead of passing in the files or directories I want to delete, to delete everything that does not match a specific file name in the directory?</p>
  
  <p>For example, If I have 3 files in directory "dir":</p>
  
  <pre><code>dir/a.js
  dir/b.js
  dir/c.js
  </code></pre>
  
  <p>Sample Pseudocode of what I want to do, (delete everything in /dir/ thats not a.js:</p>
  
  <pre><code>gulp.src('!./dir/a.js').pipe(clean());
  </code></pre>