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

Closes #206

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
     "chalk": "2.4.2"
   },
   "devDependencies": {
-    "@types/chai": "4.2.0",
+    "@types/chai": "4.2.9",
     "@types/chalk": "2.2.0",
     "@types/mocha": "5.2.7",
     "@types/sinon": "7.0.13",