Update del requirement from ^3.0.0 to ^4.0.0 (#8)

Updates the requirements on [del](https://github.com/sindresorhus/del) to permit the latest version.
- [Release notes](https://github.com/sindresorhus/del/releases)
- [Commits](sindresorhus/del@v3.0.0...v4.0.0)

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

Author: dependabot[bot]

package.json

@@ -25,7 +25,7 @@
     "url": "https://github.com/huiyifyj/Proxy-pac.js/issues"
   },
   "devDependencies": {
-    "del": "^3.0.0",
+    "del": "^4.0.0",
     "gulp": "^4.0.0",
     "gulp-concat": "^2.6.1",
     "gulp-header": "^2.0.7",