Upgrade to gulp 4.0.

.gitignore

@@ -25,4 +25,3 @@ build.properties
 
 # NPM
 node_modules
-package-lock.json

gulpfile.js

@@ -1,7 +1,7 @@
-var gulp       = require('gulp');
-var del        = require('del');
-var uglify     = require('gulp-uglify');
-var concat     = require('gulp-concat');
+const { series, src, watch, dest} = require('gulp');
+const del             = require('del');
+const uglify          = require('gulp-uglify');
+const concat          = require('gulp-concat');
 
 var paths = {
     minified: 'contao-leaflet.js',
@@ -9,20 +9,19 @@ var paths = {
     dest:     'src/Bundle/Resources/public/js'
 };
 
-gulp.task('clear', function() {
+function cleanTask (cb) {
     del([paths.dest + '/' + paths.minified]);
-});
+    cb();
+}
 
-gulp.task('scripts', ['clear'], function() {
-    return gulp.src(paths.scripts)
+const buildTask = series(cleanTask, function (cb) {
+    return src(paths.scripts)
         .pipe(concat(paths.minified))
         .pipe(uglify())
-        .pipe(gulp.dest(paths.dest));
+        .pipe(dest(paths.dest));
 });
 
-
-gulp.task('default', ['scripts']);
-
-gulp.task('watch', function() {
-   gulp.watch(paths.scripts, ['scripts']);
-});
+exports.clean   = cleanTask;
+exports.watch   = watch(paths.scripts, buildTask);
+exports.build   = buildTask;
+exports.default = buildTask;

package.json

@@ -5,9 +5,10 @@
   "main": "gulpfile.js",
   "dependencies": {
     "del": "^3.0.0",
-    "gulp": "^3.9.1",
-    "gulp-concat": "^2.6.0",
-    "gulp-uglify": "^3.0.0"
+    "gulp": "^4.0.0",
+    "gulp-cli": "^2.0.1",
+    "gulp-concat": "^2.6.1",
+    "gulp-uglify": "^3.0.1"
   },
   "devDependencies": {},
   "scripts": {
@@ -23,7 +24,7 @@
     "Maps"
   ],
   "author": "netzmacht David Molineus",
-  "license": "LGPL-3.0",
+  "license": "LGPL-3.0-or-later",
   "bugs": {
     "url": "https://github.com/netzmacht/contao-leaflet-maps/issues"
   },