Issue 5480 - Add "watch" task to website-defaults gulpfile

gulpfile.js

 /*!
  * This file is part of website-defaults
  * Copyright (C) 2016-present eyeo GmbH
  *
  * website-defaults is free software: you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as published by
  * the Free Software Foundation, either version 3 of the License, or
  * (at your option) any later version.
  *
  * website-defaults is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with website-defaults.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 const gulp = require("gulp");
 const sass = require("gulp-sass");
 
 gulp.task("scss", function ()
 {
   return gulp.src("./scss/main.scss")
     .pipe(sass().on("error", sass.logError))
     .pipe(gulp.dest("./static/css/"));
 });
 
-gulp.task("default", ["scss"]);
+gulp.task("watch", function ()
+{
+  gulp.watch("./scss/**/*.scss", ["scss"]);
+});
+
+gulp.task("default", ["scss", "watch"]);