chore(deps): update dependency google-api-core to v2 (#973)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [google-api-core](https://togithub.com/googleapis/python-api-core) | `==1.31.1` -> `==2.0.0` | [![age](https://badges.renovateapi.com/packages/pypi/google-api-core/2.0.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/google-api-core/2.0.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/google-api-core/2.0.0/compatibility-slim/1.31.1)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/google-api-core/2.0.0/confidence-slim/1.31.1)](https://docs.renovatebot.com/merge-confidence/) |

---

### Release Notes

<details>
<summary>googleapis/python-api-core</summary>

### [`v2.0.0`](https://togithub.com/googleapis/python-api-core/blob/master/CHANGELOG.md#&#8203;200-httpswwwgithubcomgoogleapispython-api-corecomparev200-b1v200-2021-08-18)

[Compare Source](https://togithub.com/googleapis/python-api-core/compare/v1.31.2...v2.0.0)

##### ⚠ BREAKING CHANGES

-   drop support for Python 2.7 / 3.5 ([#&#8203;212](https://www.togithub.com/googleapis/python-api-core/issues/212)) ([a30f004](https://www.github.com/googleapis/python-api-core/commit/a30f004e74f709d46e905dd819c71f43354e9ac9))

##### Bug Fixes

-   bump grpcio version to use stable aio API ([#&#8203;234](https://www.togithub.com/googleapis/python-api-core/issues/234)) ([bdbf889](https://www.github.com/googleapis/python-api-core/commit/bdbf889210b709d7c1945f2160bcba9161b4dd2e))
-   strip trailing \_ from field mask paths ([#&#8203;228](https://www.togithub.com/googleapis/python-api-core/issues/228)) ([ff6ef1b](https://www.github.com/googleapis/python-api-core/commit/ff6ef1bd07fa68307b7c82c910416d770e7b3416))

### [`v1.31.2`](https://togithub.com/googleapis/python-api-core/releases/v1.31.2)

[Compare Source](https://togithub.com/googleapis/python-api-core/compare/v1.31.1...v1.31.2)

##### Bug Fixes

-   strip trailing \_ from field mask paths ([#&#8203;228](https://www.togithub.com/googleapis/python-api-core/issues/228)) ([ff6ef1b](https://www.github.com/googleapis/python-api-core/commit/ff6ef1bd07fa68307b7c82c910416d770e7b3416))

</details>

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Author: renovate-bot

requirements.txt

@@ -1,5 +1,5 @@
 click==8.0.1
-google-api-core==1.31.1
+google-api-core==2.0.0
 googleapis-common-protos==1.53.0
 jinja2==3.0.1
 MarkupSafe==2.0.1