build(deps-dev): bump del from 2.2.2 to 6.0.0

Bumps [del](https://github.com/sindresorhus/del) from 2.2.2 to 6.0.0.
- [Release notes](https://github.com/sindresorhus/del/releases)
- [Commits](sindresorhus/del@v2.2.2...v6.0.0)

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

package.json

@@ -93,7 +93,7 @@
     "chai-as-promised": "^7.0.0",
     "chalk": "^4.1.1",
     "child-process-promise": "^2.2.1",
-    "del": "^2.2.1",
+    "del": "^6.0.0",
     "eslint": "^6.8.0",
     "firebase-token-generator": "^2.0.0",
     "gulp": "^4.0.2",