Switch go Gulp 4 for builds

gulpfile.js

@@ -16,14 +16,12 @@ gulp.task('prepare-release', function() {
             .pipe(tar('filter-visitors-by-operator-code-plugin-' + version + '.tar'))
             .pipe(gzip())
     )
-    .pipe(chmod(644))
+    .pipe(chmod(0644))
     .pipe(gulp.dest('release'));
 });
 
 // Builds and packs plugins sources
-gulp.task('default', ['prepare-release'], function() {
-    // The "default" task is just an alias for "prepare-release" task.
-});
+gulp.task('default', gulp.series('prepare-release'));
 
 /**
  * Returns files stream with the plugin sources.

package.json

@@ -7,12 +7,12 @@
         "url": "https://github.com/mibew/filter-visitors-by-operator-code-plugin/issues"
     },
     "devDependencies": {
-        "gulp": "~3.8.10",
+        "gulp": "~4.0.0",
         "event-stream": "~3.1.7",
         "gulp-zip": "~2.0.2",
-        "gulp-tar": "~1.3.0",
+        "gulp-tar": "~3.1.0",
         "gulp-gzip": "~0.0.8",
-        "gulp-chmod": "~1.2.0",
+        "gulp-chmod": "~3.0.0",
         "gulp-rename": "~1.2.0"
     }
-}
+}