fix(deps): update dependency sinon to v9 (#592)

Author: renovate-bot

package.json

@@ -88,7 +88,7 @@
     "c8": "^7.0.0",
     "prettier": "^1.17.1",
     "proxyquire": "^2.1.0",
-    "sinon": "^8.0.0",
+    "sinon": "^9.0.0",
     "tmp": "0.1.0",
     "typescript": "3.6.4"
   }

samples/package.json

@@ -15,7 +15,7 @@
   },
   "dependencies": {
     "@google-cloud/datastore": "^5.0.5",
-    "sinon": "^8.0.0"
+    "sinon": "^9.0.0"
   },
   "devDependencies": {
     "chai": "^4.2.0",