chore(package): update sinon to version 2.3.8

Closes #23

Author: greenkeeper[bot]

package.json

@@ -12,7 +12,7 @@
     "istanbul": "~0.4.5",
     "pre-commit": "~1.2.0",
     "mocha": "~3.3.0",
-    "sinon": "~1.17.6",
+    "sinon": "~2.3.8",
     "sinon-chai": "~2.8.0",
     "chai": "~3.5.0",
     "request": "~2.80.0"