chore(package): update sinon to version 9.0.0

Closes #352

Author: greenkeeper[bot]

package.json

@@ -60,7 +60,7 @@
     "npm-run-all": "^4.1.5",
     "nyc": "^13.1.0",
     "proxyquire": "^2.1.0",
-    "sinon": "^7.2.2",
+    "sinon": "^9.0.0",
     "strip-ansi": "^5.0.0",
     "stylelint": "^9.9.0",
     "stylelint-config-standard": "^18.2.0",