chore(package): update sinon to version 9.0.0

Closes #10

Author: greenkeeper[bot]

package.json

@@ -13,7 +13,7 @@
   "devDependencies": {
     "chai": "4.2.0",
     "mocha": "6.0.2",
-    "sinon": "7.3.1"
+    "sinon": "9.0.0"
   },
   "scripts": {
     "start": "echo nothing to start here, try test",