Upgrade Chai

Author: jakezatecky

package.json

@@ -34,7 +34,7 @@
     "babel-preset-react": "^6.11.1",
     "babel-preset-stage-2": "^6.5.0",
     "browser-sync": "^2.18.6",
-    "chai": "^3.5.0",
+    "chai": "^4.0.0",
     "enzyme": "^2.7.1",
     "eslint": "^3.15.0",
     "eslint-config-airbnb": "^15.0.0",