Update dependency google-auth to v1.11.2 (#3079)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [google-auth](https://togithub.com/googleapis/google-auth-library-python) | patch | `==1.11.1` -> `==1.11.2` |
| [google-auth](https://togithub.com/googleapis/google-auth-library-python) | patch | `==1.11.0` -> `==1.11.2` |

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### Release Notes

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

### [`v1.11.2`](https://togithub.com/googleapis/google-auth-library-python/blob/master/CHANGELOG.md#&#8203;1112httpswwwgithubcomgoogleapisgoogle-auth-library-pythoncomparev1111v1112-2020-02-14)

[Compare Source](https://togithub.com/googleapis/google-auth-library-python/compare/v1.11.1...v1.11.2)

</details>

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endpoints/bookstore-grpc-transcoding/requirements.txt

@@ -1,5 +1,5 @@
 grpcio==1.27.1
 grpcio-tools==1.27.1
-google-auth==1.11.0
+google-auth==1.11.2
 six==1.14.0
 googleapis-common-protos==1.51.0

endpoints/bookstore-grpc/requirements.txt

@@ -1,4 +1,4 @@
 grpcio==1.27.1
 grpcio-tools==1.27.1
-google-auth==1.11.1
+google-auth==1.11.2
 six==1.14.0