chore(deps): update dependency google-cloud-documentai to v0.5.0 (#155)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [google-cloud-documentai](https://togithub.com/googleapis/python-documentai) | `==0.4.0` -> `==0.5.0` | [![age](https://badges.renovateapi.com/packages/pypi/google-cloud-documentai/0.5.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/google-cloud-documentai/0.5.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/google-cloud-documentai/0.5.0/compatibility-slim/0.4.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/google-cloud-documentai/0.5.0/confidence-slim/0.4.0)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

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

### [`v0.5.0`](https://togithub.com/googleapis/python-documentai/blob/master/CHANGELOG.md#&#8203;050-httpswwwgithubcomgoogleapispython-documentaicomparev040v050-2021-05-28)

[Compare Source](https://togithub.com/googleapis/python-documentai/compare/v0.4.0...v0.5.0)

##### Features

-   add confidence field to the PageAnchor.PageRef in document.proto. ([be671a8](https://www.github.com/googleapis/python-documentai/commit/be671a832839d6efeae76d168b7913a9408572b4))
-   support self-signed JWT flow for service accounts ([be671a8](https://www.github.com/googleapis/python-documentai/commit/be671a832839d6efeae76d168b7913a9408572b4))
-   Use non-regionalized default host name for documentai.googleapis.com ([be671a8](https://www.github.com/googleapis/python-documentai/commit/be671a832839d6efeae76d168b7913a9408572b4))

##### Bug Fixes

-   add async client to %name\_%version/init.py ([be671a8](https://www.github.com/googleapis/python-documentai/commit/be671a832839d6efeae76d168b7913a9408572b4))
-   Parsing pages, but should be paragraphs ([#&#8203;147](https://www.github.com/googleapis/python-documentai/issues/147)) ([c4aca1b](https://www.github.com/googleapis/python-documentai/commit/c4aca1bc1c01b3e1fdcc644eaf8922552c6c99a7))

</details>

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document_ai/snippets/requirements.txt

@@ -1,2 +1,2 @@
-google-cloud-documentai==0.4.0
+google-cloud-documentai==0.5.0
 google-cloud-storage==1.37.1