chore(deps): update dependency google-cloud-kms to v2 (#29)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [google-cloud-kms](https://togithub.com/googleapis/python-kms) | major | `==1.4.0` -> `==2.0.0` |

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### Release Notes

<details>
<summary>googleapis/python-kms</summary>

### [`v2.0.0`](https://togithub.com/googleapis/python-kms/blob/master/CHANGELOG.md#&#8203;200-httpswwwgithubcomgoogleapispython-kmscomparev140v200-2020-07-30)

[Compare Source](https://togithub.com/googleapis/python-kms/compare/v1.4.0...v2.0.0)

##### ⚠ BREAKING CHANGES

-   migrate to microgenerator. ([#&#8203;16](https://togithub.com/googleapis/python-kms/issues/16))

##### Features

-   migrate to microgenerator. See [Migration Guide](https://togithub.com/googleapis/python-kms/blob/release-v2.0.0/UPGRADING.md). ([#&#8203;16](https://www.github.com/googleapis/python-kms/issues/16)) ([605f757](https://www.github.com/googleapis/python-kms/commit/605f7577a9a9f1a2b39fa69da7e250b5f70e945e))

</details>

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kms/snippets/requirements.txt

@@ -1,2 +1,2 @@
-google-cloud-kms==1.4.0
-cryptography==3.1
+google-cloud-kms==2.0.0
+cryptography==3.1