chore(package): update sinon to version 4.0.0

Closes #152

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
     "mocha": "~3.5.0",
     "nyc": "^11.0.0",
     "request": "^2.49.0",
-    "sinon": "~2.4.0",
+    "sinon": "~4.0.0",
     "sinon-chai": "~2.13.0"
   },
   "directories": {