chore(package): update sinon to version 2.4.0

Closes #9

Author: greenkeeper[bot]

package.json

@@ -33,6 +33,6 @@
     "mocha": "^3.1.2",
     "redux": "^3.0.4",
     "require-dir": "^0.3.0",
-    "sinon": "^1.17.2"
+    "sinon": "^2.4.0"
   }
 }