chore(deps): update dependency @types/mocha to v8 (#329)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [@types/mocha](https://togithub.com/DefinitelyTyped/DefinitelyTyped) | devDependencies | major | [`^7.0.0` -> `^8.0.0`](https://renovatebot.com/diffs/npm/@types%2fmocha/7.0.2/8.0.0) |

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packages/google-cloud-resourcemanager/package.json

@@ -49,7 +49,7 @@
     "@google-cloud/promisify": "^2.0.0"
   },
   "devDependencies": {
-    "@types/mocha": "^7.0.0",
+    "@types/mocha": "^8.0.0",
     "@types/proxyquire": "^1.3.28",
     "@types/uuid": "^8.0.0",
     "arrify": "^2.0.0",