chore(package): update sinon-chai to version 3.4.0

Closes #26

Author: greenkeeper[bot]

package.json

@@ -46,7 +46,7 @@
     "express": "^4.14.0",
     "mocha": "^3.3.0",
     "sinon": "^2.1.0",
-    "sinon-chai": "^2.9.0",
+    "sinon-chai": "^3.4.0",
     "supertest": "^2.0.1"
   }
 }