Bump gulp from 3.5.6 to 4.0.2

Bumps [gulp](https://github.com/gulpjs/gulp) from 3.5.6 to 4.0.2.
- [Release notes](https://github.com/gulpjs/gulp/releases)
- [Changelog](https://github.com/gulpjs/gulp/blob/master/CHANGELOG.md)
- [Commits](https://github.com/gulpjs/gulp/commits/v4.0.2)

Signed-off-by: dependabot-preview[bot] <[email protected]>

package.json

@@ -33,7 +33,7 @@
   },
   "devDependencies": {
     "coffee-script": "~1.7.1",
-    "gulp": "~3.5.5",
+    "gulp": "~4.0.2",
     "gulp-coffee": "~1.4.1",
     "gulp-clean": "~0.2.4",
     "gulp-mocha": "~0.4.1",