fix(deps): update dependency google-auth-library to v6 (#660)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [google-auth-library](https://togithub.com/googleapis/google-auth-library-nodejs) | dependencies | major | [`^5.8.0` -> `^6.0.0`](https://renovatebot.com/diffs/npm/google-auth-library/5.10.1/6.0.0) |

---

### Release Notes

<details>
<summary>googleapis/google-auth-library-nodejs</summary>

### [`v6.0.0`](https://togithub.com/googleapis/google-auth-library-nodejs/blob/master/CHANGELOG.md#&#8203;600-httpswwwgithubcomgoogleapisgoogle-auth-library-nodejscomparev5101v600-2020-03-26)

[Compare Source](https://togithub.com/googleapis/google-auth-library-nodejs/compare/v5.10.1...v6.0.0)

##### ⚠ BREAKING CHANGES

-   typescript@3.7.x introduced some breaking changes in
    generated code.
-   require node 10 in engines field ([#&#8203;926](https://togithub.com/googleapis/google-auth-library-nodejs/issues/926))
-   remove deprecated methods ([#&#8203;906](https://togithub.com/googleapis/google-auth-library-nodejs/issues/906))

##### Features

-   require node 10 in engines field ([#&#8203;926](https://www.github.com/googleapis/google-auth-library-nodejs/issues/926)) ([d89c59a](https://www.github.com/googleapis/google-auth-library-nodejs/commit/d89c59a316e9ca5b8c351128ee3e2d91e9729d5c))

##### Bug Fixes

-   do not warn for SDK creds ([#&#8203;905](https://www.github.com/googleapis/google-auth-library-nodejs/issues/905)) ([9536840](https://www.github.com/googleapis/google-auth-library-nodejs/commit/9536840f88e77f747bbbc2c1b5b4289018fc23c9))
-   use iamcredentials API to sign blobs ([#&#8203;908](https://www.github.com/googleapis/google-auth-library-nodejs/issues/908)) ([7b8e4c5](https://www.github.com/googleapis/google-auth-library-nodejs/commit/7b8e4c52e31bb3d448c3ff8c05002188900eaa04))
-   **deps:** update dependency gaxios to v3 ([#&#8203;917](https://www.github.com/googleapis/google-auth-library-nodejs/issues/917)) ([1f4bf61](https://www.github.com/googleapis/google-auth-library-nodejs/commit/1f4bf6128a0dcf22cfe1ec492b2192f513836cb2))
-   **deps:** update dependency gcp-metadata to v4 ([#&#8203;918](https://www.github.com/googleapis/google-auth-library-nodejs/issues/918)) ([d337131](https://www.github.com/googleapis/google-auth-library-nodejs/commit/d337131d009cc1f8182f7a1f8a9034433ee3fbf7))
-   **types:** add additional fields to TokenInfo ([#&#8203;907](https://www.github.com/googleapis/google-auth-library-nodejs/issues/907)) ([5b48eb8](https://www.github.com/googleapis/google-auth-library-nodejs/commit/5b48eb86c108c47d317a0eb96b47c0cae86f98cb))

##### Build System

-   update to latest gts and TypeScript ([#&#8203;927](https://www.github.com/googleapis/google-auth-library-nodejs/issues/927)) ([e11e18c](https://www.github.com/googleapis/google-auth-library-nodejs/commit/e11e18cb33eb60a666980d061c54bb8891cdd242))

##### Miscellaneous Chores

-   remove deprecated methods ([#&#8203;906](https://www.github.com/googleapis/google-auth-library-nodejs/issues/906)) ([f453fb7](https://www.github.com/googleapis/google-auth-library-nodejs/commit/f453fb7d8355e6dc74800b18d6f43c4e91d4acc9))

##### [5.10.1](https://www.github.com/googleapis/google-auth-library-nodejs/compare/v5.10.0...v5.10.1) (2020-02-25)

##### Bug Fixes

-   if GCF environment detected, increase library timeout ([#&#8203;899](https://www.github.com/googleapis/google-auth-library-nodejs/issues/899)) ([2577ff2](https://www.github.com/googleapis/google-auth-library-nodejs/commit/2577ff28bf22dfc58bd09e7365471c16f359f109))

</details>

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samples/package.json

@@ -18,7 +18,7 @@
   "dependencies": {
     "@google-cloud/bigquery": "^4.7.0",
     "@google-cloud/storage": "^4.0.0",
-    "google-auth-library": "^5.8.0",
+    "google-auth-library": "^6.0.0",
     "readline-promise": "^1.0.4",
     "yargs": "^15.0.0"
   },