fix(deps): update dependency is-reachable to v5 (#2010)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [is-reachable](https://togithub.com/sindresorhus/is-reachable) | dependencies | major | [`^4.0.0` -> `^5.0.0`](https://renovatebot.com/diffs/npm/is-reachable/4.0.0/5.0.0) |

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### Release Notes

<details>
<summary>sindresorhus/is-reachable</summary>

### [`v5.0.0`](https://togithub.com/sindresorhus/is-reachable/releases/v5.0.0)

[Compare Source](https://togithub.com/sindresorhus/is-reachable/compare/v4.0.0...v5.0.0)

##### Breaking

-   Require Node.js 10 ([#&#8203;48](https://togithub.com/sindresorhus/is-reachable/issues/48))  [`50d61e8`](https://togithub.com/sindresorhus/is-reachable/commit/50d61e8)

##### Fixes

-   Fix timeout handling ([#&#8203;48](https://togithub.com/sindresorhus/is-reachable/issues/48))  [`50d61e8`](https://togithub.com/sindresorhus/is-reachable/commit/50d61e8)

</details>

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datastore/functions/package.json

@@ -15,7 +15,7 @@
   },
   "dependencies": {
     "@google-cloud/datastore": "^6.0.0",
-    "is-reachable": "^4.0.0"
+    "is-reachable": "^5.0.0"
   },
   "devDependencies": {
     "@google-cloud/functions-framework": "^1.1.1",