fix(deps): update dependency gcp-metadata to v4 (#1219)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [gcp-metadata](https://togithub.com/googleapis/gcp-metadata) | dependencies | major | [`^3.0.0` -> `^4.0.0`](https://renovatebot.com/diffs/npm/gcp-metadata/3.5.0/4.0.0) |

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### Release Notes

<details>
<summary>googleapis/gcp-metadata</summary>

### [`v4.0.0`](https://togithub.com/googleapis/gcp-metadata/blob/master/CHANGELOG.md#&#8203;400-httpswwwgithubcomgoogleapisgcp-metadatacomparev350v400-2020-03-19)

[Compare Source](https://togithub.com/googleapis/gcp-metadata/compare/v3.5.0...v4.0.0)

##### ⚠ BREAKING CHANGES

-   typescript@3.7.x has breaking changes; compiler now targets es2015
-   drops Node 8 from engines field ([#&#8203;315](https://togithub.com/googleapis/gcp-metadata/issues/315))

##### Features

-   drops Node 8 from engines field ([#&#8203;315](https://www.github.com/googleapis/gcp-metadata/issues/315)) ([acb6233](https://www.github.com/googleapis/gcp-metadata/commit/acb62337e8ba7f0b259ae4e553f19c5786207d84))

##### Build System

-   switch to latest typescirpt/gts ([#&#8203;317](https://www.github.com/googleapis/gcp-metadata/issues/317)) ([fbb7158](https://www.github.com/googleapis/gcp-metadata/commit/fbb7158be62c9f1949b69079e35113be1e10495c))

</details>

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package.json

@@ -104,7 +104,7 @@
     "console-log-level": "^1.4.0",
     "continuation-local-storage": "^3.2.1",
     "extend": "^3.0.2",
-    "gcp-metadata": "^3.0.0",
+    "gcp-metadata": "^4.0.0",
     "hex2dec": "^1.0.1",
     "is": "^3.2.0",
     "methods": "^1.1.1",