chore(package): update @types/chai to version 4.2.8

Author: greenkeeper[bot]

package.json

@@ -46,7 +46,7 @@
     "graphql-subscriptions": "^1.0.0"
   },
   "devDependencies": {
-    "@types/chai": "^4.1.6",
+    "@types/chai": "^4.2.8",
     "@types/ioredis": "4.14.1",
     "@types/chai-as-promised": "7.1.1",
     "@types/mocha": "^5.2.5",