Support gulp v4

At this moment all tasks gives error: "Task function must be specified".

Author: Volodymyr

gulpfile.js

@@ -114,9 +114,6 @@ else {
  Gulp tasks
  ========================================================================== */
 
-// Default task. Run compilation for all themes
-gulp.task('default', ['less']);
-
 // Less task
 gulp.task('less', function() {
 // Console info
@@ -221,3 +218,6 @@ gulp.task('clean', function (cb) {
  console.log('Please add your defined Theme ex: --luma'.red);
  }
 });
+
+// Default task. Run compilation for all themes
+gulp.task('default', gulp.series('less'));