chore(package): update sinon to version 2.3.7

Closes #7

Author: greenkeeper[bot]

package.json

@@ -13,7 +13,7 @@
     "mocha": "~3.2.0",
     "mocha-lcov-reporter": "~1.2.0",
     "pre-commit": "~1.2.0",
-    "sinon": "~1.17.6",
+    "sinon": "~2.3.7",
     "sinon-chai": "~2.8.0"
   },
   "scripts": {