Bump gulp from 3.9.1 to 4.0.2

Bumps [gulp](https://github.com/gulpjs/gulp) from 3.9.1 to 4.0.2.
- [Release notes](https://github.com/gulpjs/gulp/releases)
- [Changelog](https://github.com/gulpjs/gulp/blob/master/CHANGELOG.md)
- [Commits](gulpjs/gulp@v3.9.1...v4.0.2)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -45,7 +45,7 @@
     "fs-extra": "^3.0.1",
     "ftp-deploy": "^2.3.6",
     "github": "^9.2.0",
-    "gulp": "^3.9.1",
+    "gulp": "^4.0.2",
     "gulp-babel": "^6.1.2",
     "gulp-clean": "^0.3.2",
     "gulp-concat": "^2.6.1",