updated gulp to V4

sites/all/themes/gui/materiobasetheme/gulpfile.js

@@ -12,31 +12,30 @@ function handleError(err) {
   // this.emit('end');
 }
 
-gulp.task('scripts', function () {
-    gulp.src('./js/script.js')
-        .pipe(jsmin())
-        .pipe(rename({suffix: '.min'}))
-        .pipe(gulp.dest('./js/'));
+gulp.task('scripts', done => {
+  gulp.src('./js/script.js')
+      .pipe(jsmin())
+      .pipe(rename({suffix: '.min'}))
+      .pipe(gulp.dest('./js/'));
+  done();
 });
 
-gulp.task('styles', function () {
+gulp.task('styles', done => {
   gulp.src('./scss/styles.scss')
     .pipe(sass().on('error', sass.logError))
     // .pipe(gulp.dest('./css/'));
 
   // gulp.src('./css/*.css')
     .pipe(autoprefixer({
-        browsers: ['last 2 versions'],
         cascade: false
     })).on('error', handleError)
     .pipe(gulp.dest('./css/'));
-});
-
-gulp.task('default', function () {
+  done();
 });
 
 // default gulp task
-gulp.task('default', ['scripts', 'styles'], function() {
-  gulp.watch('./scss/*.scss', ['styles']);
-  gulp.watch('./js/script.js', ['scripts']);
-});
+gulp.task('default', gulp.series('scripts', 'styles', function(done) {
+  gulp.watch('./scss/*.scss', gulp.series('styles'));
+  gulp.watch('./js/script.js', gulp.series('scripts'));
+  done()
+}));