chore(deps): update dependency google-api-core to v1.27.0 (#889)

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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) | `==1.26.3` -> `==1.27.0` | [![age](https://badges.renovateapi.com/packages/pypi/google-api-core/1.27.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/google-api-core/1.27.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/google-api-core/1.27.0/compatibility-slim/1.26.3)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/google-api-core/1.27.0/confidence-slim/1.26.3)](https://docs.renovatebot.com/merge-confidence/) |

---

### Release Notes

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

### [`v1.27.0`](https://togithub.com/googleapis/python-api-core/blob/master/CHANGELOG.md#&#8203;1270-httpswwwgithubcomgoogleapispython-api-corecomparev1263v1270-2021-05-18)

[Compare Source](https://togithub.com/googleapis/python-api-core/compare/v1.26.3...v1.27.0)

##### Features

-   Add support for `rest/` token in `x-goog-api-client` header ([#&#8203;189](https://www.github.com/googleapis/python-api-core/issues/189)) ([15aca6b](https://www.github.com/googleapis/python-api-core/commit/15aca6b288b2ec5ce0251e442e1dfa7f52e1b124))
-   retry google.auth TransportError and requests ConnectionError ([#&#8203;178](https://www.github.com/googleapis/python-api-core/issues/178)) ([6ae04a8](https://www.github.com/googleapis/python-api-core/commit/6ae04a8d134fffe13f06081e15f9723c1b2ea334))

##### [1.26.3](https://www.github.com/googleapis/python-api-core/compare/v1.26.2...v1.26.3) (2021-03-25)

##### Bug Fixes

-   skip empty policy bindings in `len()` and `iter()` ([#&#8203;159](https://www.github.com/googleapis/python-api-core/issues/159)) ([9eaa786](https://www.github.com/googleapis/python-api-core/commit/9eaa7868164a7e98792de24d2be97f79fba22322))

##### Documentation

-   update python contributing guide ([#&#8203;147](https://www.github.com/googleapis/python-api-core/issues/147)) ([1d76b57](https://www.github.com/googleapis/python-api-core/commit/1d76b57d1f218f7885f85dc7c052bad1ad3857ac))

##### [1.26.2](https://www.github.com/googleapis/python-api-core/compare/v1.26.1...v1.26.2) (2021-03-23)

##### Bug Fixes

-   save empty IAM policy bindings ([#&#8203;155](https://www.github.com/googleapis/python-api-core/issues/155)) ([536c2ca](https://www.github.com/googleapis/python-api-core/commit/536c2cad814b8fa8cd346a3d7bd5f6b9889c4a6f))

##### [1.26.1](https://www.github.com/googleapis/python-api-core/compare/v1.26.0...v1.26.1) (2021-02-12)

##### Bug Fixes

-   add operation name to x-goog-request-params in async client ([#&#8203;137](https://www.github.com/googleapis/python-api-core/issues/137)) ([7271b23](https://www.github.com/googleapis/python-api-core/commit/7271b23afddb032e49e957525704d0cd5bfa4c65))

</details>

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packages/gapic-generator/requirements.txt

@@ -1,5 +1,5 @@
 click==8.0.0
-google-api-core==1.26.3
+google-api-core==1.27.0
 googleapis-common-protos==1.53.0
 jinja2==3.0.1
 MarkupSafe==2.0.1