Bug 1855373: Gulp update to v4

Changes to gulpfile to make Gulp 4 work
Removed gulp-help
update yargs to latest version to avoid potential vulnerability

Change-Id: Ia2f085372b8b8d3d40252686e183271f6b91ebe3

gulpfile.js

 // Include gulp
-var gulp = require('gulp-help')(require('gulp'));
+var gulp = require('gulp');
 
 //Polyfill so we don't need >= node 0.12
 require('es6-promise').polyfill();
@@ -22,7 +22,7 @@ themes = themes.map(function(themepath){
 });
 
 // Turn sass into css
-gulp.task('css', 'Compile SASS into CSS', function () {
+async function css () {
     var tasks = themes.map(function(themepath){
 
         console.log("Compiling CSS for " + themepath);
@@ -40,12 +40,13 @@ gulp.task('css', 'Compile SASS into CSS', function () {
     });
 
     return es.concat.apply(null, tasks);
-});
+};
 
-// Watch Files For Changes
-gulp.task('watch', 'Watch style directories and auto-compile CSS', function() {
-    gulp.watch('htdocs/theme/*/sass/**/*.scss', ['css']);
-});
+function watch() {
+    gulp.watch('htdocs/theme/*/sass/**/*.scss', gulp.series('css'));
+}
+
+gulp.task('css', css);
+gulp.task('watch', watch);
 
-// Default Task (recompile on init before watching)
-gulp.task('default', ['css', 'watch']);
+gulp.task('default', gulp.series(css, watch));
\ No newline at end of file

package.json

@@ -12,15 +12,14 @@
     "es6-promise": "^4.2.4",
     "event-stream": "3.3.4",
     "globule": "^1.0.0",
-    "gulp": "<=3.9.1",
+    "gulp": "^4.0.2",
     "gulp-autoprefixer": "^5.0.0",
     "gulp-clean-css": "^3.0.2",
-    "gulp-help": "^1.6.1",
     "gulp-if": "^2.0.2",
     "gulp-sass": "^4.0.1",
-    "node-sass": "<=4.8.3",
+    "node-sass": "^4.13.0",
     "path": "^0.11.14",
-    "yargs": "^11.0.0"
+    "yargs": "^15.1.0"
   },
   "devDependencies": {},
   "scripts": {