change gulp build to use series task (#483)

Changed gulp build to use series task

Author: wti806

gulpfile.js

@@ -335,18 +335,14 @@ gulp.task('clean', () => fse.remove(TMP_DIR));
 
 // Executes the basic tasks for the default language.
 gulp.task('default', gulp.series(
-    gulp.parallel(
-        'build-externs', 'build-ts', 'build-js',
-        'build-npm', 'build-css', 'build-css-rtl'
-    ),
+    'build-externs', 'build-ts', 'build-js',
+    'build-npm', 'build-css', 'build-css-rtl',
     'clean'
 ));
 
 // Builds everything (JS for all languages, both LTR and RTL CSS).
 gulp.task('build-all', gulp.series(
-    gulp.parallel(
-        'build-externs', 'build-ts', 'build-all-js',
-        'build-npm', 'build-css', 'build-css-rtl'
-    ),
+    'build-externs', 'build-ts', 'build-all-js',
+    'build-npm', 'build-css', 'build-css-rtl',
     'clean'
 ));