chore(package): update sinon to version 9.0.2

Closes #52

Author: greenkeeper[bot]

package.json

@@ -32,7 +32,7 @@
     "mocha": "^5.0.0",
     "nyc": "^12.0.1",
     "proxyquire": "^1.8.0",
-    "sinon": "^4.1.2",
+    "sinon": "^9.0.2",
     "sinon-chai": "^2.14.0"
   },
   "scripts": {