chore(package): update chai to version 4.1.2

Closes #69

Author: greenkeeper[bot]

package.json

@@ -49,7 +49,7 @@
     "@types/superagent": "^2.0.34",
     "@types/supertest": "^2.0.0",
     "@types/winston": "2.3.4",
-    "chai": "^3.5.0",
+    "chai": "^4.1.2",
     "codeclimate-test-reporter": "^0.4.0",
     "core-js": "^2.4.1",
     "istanbul": "^0.4.3",