Bump eslint from 6.8.0 to 7.18.0

Bumps [eslint](https://github.com/eslint/eslint) from 6.8.0 to 7.18.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](eslint/eslint@v6.8.0...v7.18.0)

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

package.json

@@ -19,7 +19,7 @@
   },
   "devDependencies": {
     "chai": "^4.2.0",
-    "eslint": "^6.7.2",
+    "eslint": "^7.18.0",
     "eslint-config-hexo": "^4.0.0",
     "hexo": "^4.0.0",
     "hexo-unique-post-path": "file:.",