Add Chai library for tests

spec/package.json

@@ -5,6 +5,7 @@
   "version": "0.1.0",
   "devDependencies": {
     "basic-auth": "^1.0.4",
+    "chai": "^4.1.2",
     "coffee-script": "^1.12.3",
     "graceful-fs": "^4.1.9",
     "mkdirp": "^0.5.1",