chore(package): update sinon to version 2.1.0

Closes #60

https://greenkeeper.io/

Author: greenkeeper[bot]

package.json

@@ -29,6 +29,6 @@
     "babel-preset-es2015-node4": "^2.1.0",
     "expect.js": "^0.3.1",
     "mocha": "^3.1.2",
-    "sinon": "^1.17.2"
+    "sinon": "^2.1.0"
   }
 }