chore(package): update sinon to version 4.0.0 (#241)

Author: greenkeeper[bot]

package.json

@@ -54,7 +54,7 @@
     "nock": "^9.0.2",
     "proxyquire": "^1.7.3",
     "should": "^13.0.0",
-    "sinon": "^3.0.0"
+    "sinon": "^4.0.0"
   },
   "files": [
     "index.js",