Merge pull request #41 from hexojs/dependabot/npm_and_yarn/chai-tw-4.2.0

Update chai requirement from ^3.5.0 to ^4.2.0

Author: segayuu

package.json

@@ -43,7 +43,7 @@
     "tildify": "^1.2.0"
   },
   "devDependencies": {
-    "chai": "^3.5.0",
+    "chai": "^4.2.0",
     "chai-as-promised": "^7.1.1",
     "eslint": "^5.9.0",
     "eslint-config-hexo": "^3.0.0",