chore(deps): update dependency chai to v4.3.9

Author: renovate[bot]

package.json

@@ -38,7 +38,7 @@
     "pad": "2.3.0"
   },
   "devDependencies": {
-    "chai": "4.3.6",
+    "chai": "4.3.9",
     "eslint": "4.19.1",
     "eslint-config-standard": "11.0.0",
     "eslint-plugin-import": "2.27.5",