Docs: add missing returns property to raw

lib/output.js

@@ -1046,6 +1046,7 @@ function jxl (options) {
  *
  * @param {Object} [options] - output options
  * @param {string} [options.depth='uchar'] - bit depth, one of: char, uchar (default), short, ushort, int, uint, float, complex, double, dpcomplex
+ * @returns {Sharp}
  * @throws {Error} Invalid options
  */
 function raw (options) {