chore(deps): update dependency google-auth to v1.14.2 [(#3724)](GoogleCloudPlatform/python-docs-samples#3724)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [google-auth](https://togithub.com/googleapis/google-auth-library-python) | patch | `==1.14.1` -> `==1.14.2` |

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### Release Notes

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

### [`v1.14.2`](https://togithub.com/googleapis/google-auth-library-python/blob/master/CHANGELOG.md#&#8203;1142-httpswwwgithubcomgoogleapisgoogle-auth-library-pythoncomparev1141v1142-2020-05-07)

[Compare Source](https://togithub.com/googleapis/google-auth-library-python/compare/v1.14.1...v1.14.2)

</details>

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samples/api-client/manager/requirements.txt

@@ -2,7 +2,7 @@ cryptography==2.9.2
 flaky==3.6.1
 google-api-python-client==1.8.2
 google-auth-httplib2==0.0.3
-google-auth==1.14.1
+google-auth==1.14.2
 google-cloud-iot==1.0.0
 google-cloud-pubsub==1.4.2
 paho-mqtt==1.5.0