Fix comment.

lib/middleware.js

@@ -15,7 +15,7 @@ var imports = {};
  *
  *    `force`       Always re-compile
  *    `debug`       Output debugging information
- *    `src`         Source directory used to find .styl files
+ *    `src`         Source directory used to find .scss files
  *    `dest`        Destination directory used to output .css files
  *                  when undefined defaults to `src`.
  *    `outputStyle` Sass output style (nested,expanded, compact or compressed)