title: TypeError: dest.on is not a function in gulp
body: <p>When I edit theme .yml files in my themes source folder, I get this error. This does not happen when I edit scss or template .yml files from the template folder, only in the main folder. Others that had this error use things like webpack what I don't have. The gulp task for copy_theme_files is the same as other tasks with the difference that it has no return because I didn't know how to return there with two gulp.src functions.</p>
  
  <pre><code>gulp.task('copy_theme_files', function() {
      console.log('[copy_theme_files] Console Log: copy '+paths.themeSrc+' to '+paths.themeDest);
      gulp.src(paths.themeSrc)
          .pipe(gulp.dest(paths.themeDest));
      gulp.src(paths.root + '/*.{png,ico,svg}')
          .pipe(paths.themeDest);
  });
  </code></pre>
  
  <p>Full gulpfile.js <a href="https://pastebin.com/NWt2uMwV" rel="nofollow noreferrer">https://pastebin.com/NWt2uMwV</a></p>
  
  <p>Error Output:</p>
  
  <pre><code>[00:37:58] Using gulpfile /var/www/themes.src/mytheme.src/gulpfile.js
  [00:37:58] Starting 'watch'...
  [00:38:20] Starting 'copy_theme_files'...
  [copy_theme_files] Console Log: copy *.{yml,theme,php,png,jpg,gif,svg,ico},.gitkeep to build
  [00:38:20] 'copy_theme_files' errored after 23 ms
  [00:38:20] TypeError: dest.on is not a function
      at DestroyableTransform.Readable.pipe (/var/www/themes.src/mytheme.src/node_modules/readable-stream/lib/_stream_readable.js:564:8)
      at /var/www/themes.src/mytheme.src/gulpfile.js:122:10
      at taskWrapper (/var/www/themes.src/mytheme.src/node_modules/undertaker/lib/set-task.js:13:15)
      at bound (domain.js:395:14)
      at runBound (domain.js:408:12)
      at asyncRunner (/var/www/themes.src/mytheme.src/node_modules/async-done/index.js:55:18)
      at process._tickCallback (internal/process/next_tick.js:61:11)
  [00:38:20] Starting 'copy_includes'...
  [copy_includes] Console Log: copy includes/**/*.*,includes/**/.gitkeep to build/includes
  [00:38:20] Finished 'copy_includes' after 7.41 ms
  [00:38:20] Starting 'copy_build'...
  [copy_build] Console Log: copy build/**/*.*,build/**/.gitkeep to ../../web/themes/local/mytheme
  [00:38:20] Finished 'copy_build' after 60 ms
  </code></pre>
  
  <p>Other tasks run fine</p>
  
  <pre><code>[00:41:06] Starting 'copy_templates'...
  [copy_templates] Console Log: copy templates/**/*.twig,templates/**/.gitkeep to build/templates
  [00:41:08] Finished 'copy_templates' after 1.86 s
  [00:41:08] Starting 'copy_build'...
  [copy_build] Console Log: copy build/**/*.*,build/**/.gitkeep to ../../web/themes/local/mytheme
  [00:41:09] Finished 'copy_build' after 326 ms
  </code></pre>