fails if output directory doesn't exist

[mvolkmann]

Suppose my input files are in a directory named input, my .scss files are in input/assets and the directory _site does not yet exist. If I configure this plugin as follows and try to build the site, it fails with an error saying that _site/assets doesn't exist.

  eleventyConfig.addPlugin(sassPlugin, {
    watch: 'input/**/*.{scss,sass}'
  });

If I manually create the _site/assets directory and then build the site, it works. I think this plugin needs to create any output directories for which it plans to write .css files.