chore(package): update sinon to version 8.1.0

Closes #59

Author: greenkeeper[bot]

package.json

@@ -60,7 +60,7 @@
     "react-dom": "^16.8.6",
     "rimraf": "^2.6.3",
     "safe-publish-latest": "^1.1.2",
-    "sinon": "^6.3.5",
+    "sinon": "^8.1.0",
     "sinon-sandbox": "^2.0.5"
   },
   "peerDependencies": {