Merge pull request #113 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

@@ -25,7 +25,7 @@
   ],
   "license": "MIT",
   "devDependencies": {
-    "chai": "^3.5.0",
+    "chai": "^4.2.0",
     "eslint": "^5.6.1",
     "eslint-config-hexo": "^3.0.0",
     "istanbul": "^0.4.3",