Bump hexo from 3.9.0 to 4.0.0 (#73)

Bumps [hexo](https://github.com/hexojs/hexo) from 3.9.0 to 4.0.0.
- [Release notes](https://github.com/hexojs/hexo/releases)
- [Commits](hexojs/hexo@3.9.0...4.0.0)

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

package.json

@@ -38,7 +38,7 @@
     "cheerio": "^0.22.0",
     "eslint": "^6.0.1",
     "eslint-config-hexo": "^3.0.0",
-    "hexo": "^3.0.0",
+    "hexo": "^4.0.0",
     "mocha": "^6.0.2",
     "nyc": "^14.1.0"
   },