chore(package): update chai to version 4.1.2

Closes #30

Author: greenkeeper[bot]

package.json

@@ -29,7 +29,7 @@
     "nodeos-mount": "^0.3.1"
   },
   "devDependencies": {
-    "chai": "^3.5.0",
+    "chai": "^4.1.2",
     "errno-codes": "^1.0.2",
     "istanbul": "^0.4.5",
     "mocha": "^3.0.2",