chore(package): update @types/chai to version 4.2.9

Closes #14

Author: greenkeeper[bot]

package.json

@@ -43,7 +43,7 @@
     "axios": "0.19.0"
   },
   "devDependencies": {
-    "@types/chai": "4.1.7",
+    "@types/chai": "4.2.9",
     "@types/mocha": "5.2.7",
     "@types/nock": "10.0.3",
     "@types/rewire": "2.5.28",