build(deps-dev): bump eslint from 4.19.1 to 6.2.0 in /site

Bumps [eslint](https://github.com/eslint/eslint) from 4.19.1 to 6.2.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](eslint/eslint@v4.19.1...v6.2.0)

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

site/package.json

@@ -25,8 +25,9 @@
     "uuid": "^3.3.2"
   },
   "devDependencies": {
+    "acorn": "^6.0.0",
     "del": "^3.0.0",
-    "eslint": "^4.3.0",
+    "eslint": "^6.2.0",
     "eslint-config-hexo": "^2.0.0",
     "gulp": "^4.0.2",
     "gulp-cheerio": "^0.6.2",