Upgrade to gulp 4

gulpfile.js

@@ -33,5 +33,5 @@ gulp.task('images', function() {
 });
 
 //Building project with run sequence
-gulp.task('build-styles', ['build-css', 'images', 'build-themes']);
+gulp.task("build-styles", gulp.series("build-css", "images", "build-themes"));
 

package.json

@@ -44,11 +44,11 @@
     "core-js": "^3.6.5",
     "eslint": "^6.7.2",
     "eslint-plugin-vue": "^7.0.0-0",
-    "gulp": "^3.9.1",
+    "gulp": "^4.0.2",
     "gulp-concat": "^2.6.0",
-    "gulp-flatten": "^0.2.0",
-    "gulp-rename": "^1.2.2",
-    "gulp-uglify": "^1.5.3",
+    "gulp-flatten": "^0.4.0",
+    "gulp-rename": "^2.0.0",
+    "gulp-uglify": "^3.0.2",
     "gulp-uglifycss": "^1.0.6",
     "node-sass": "^4.12.0",
     "primeflex": "2.0.0",