Upgrade gulp requirement from ^4.0.0 to ^4.0.1 (#15)

Upgrades the requirements on [gulp](https://github.com/gulpjs/gulp) to permit the latest version.

Author: dependabot[bot]

package.json

@@ -27,7 +27,7 @@
   },
   "devDependencies": {
     "del": "^4.1.0",
-    "gulp": "^4.0.0",
+    "gulp": "^4.0.1",
     "gulp-concat": "^2.6.1",
     "gulp-header": "^2.0.7",
     "gulp-rename": "^1.4.0",