chore(deps): update dependency google-cloud-bigquery to v2.4.0 (#391)

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This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [google-cloud-bigquery](https://togithub.com/googleapis/python-bigquery) | minor | `==2.3.1` -> `==2.4.0` |

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### Release Notes

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

### [`v2.4.0`](https://togithub.com/googleapis/python-bigquery/blob/master/CHANGELOG.md#&#8203;240-httpswwwgithubcomgoogleapispython-bigquerycomparev231v240-2020-11-16)

[Compare Source](https://togithub.com/googleapis/python-bigquery/compare/v2.3.1...v2.4.0)

##### Features

-   add progress bar to `QueryJob.to_dataframe` and `to_arrow` ([#&#8203;352](https://www.github.com/googleapis/python-bigquery/issues/352)) ([dc78edd](https://www.github.com/googleapis/python-bigquery/commit/dc78eddde7a6a312c8fed7bace7d64036837ab1a))
-   allow routine references ([#&#8203;378](https://www.github.com/googleapis/python-bigquery/issues/378)) ([f9480dc](https://www.github.com/googleapis/python-bigquery/commit/f9480dc2a1bc58367083176bd74725aa8b903301))

##### Bug Fixes

-   **dbapi:** allow rows to be fetched from scripts ([#&#8203;387](https://www.github.com/googleapis/python-bigquery/issues/387)) ([b899ad1](https://www.github.com/googleapis/python-bigquery/commit/b899ad12e17cb87c58d3ae46b4388d917c5743f2)), closes [#&#8203;377](https://www.github.com/googleapis/python-bigquery/issues/377)

##### Performance Improvements

-   avoid extra API calls from `to_dataframe` if all rows are cached ([#&#8203;384](https://www.github.com/googleapis/python-bigquery/issues/384)) ([c52b317](https://www.github.com/googleapis/python-bigquery/commit/c52b31789998fc0dfde07c3296650c85104d719d))
-   cache first page of `jobs.getQueryResults` rows ([#&#8203;374](https://www.github.com/googleapis/python-bigquery/issues/374)) ([86f6a51](https://www.github.com/googleapis/python-bigquery/commit/86f6a516d1c7c5dc204ab085ea2578793e6561ff))
-   use `getQueryResults` from DB-API ([#&#8203;375](https://www.github.com/googleapis/python-bigquery/issues/375)) ([30de15f](https://www.github.com/googleapis/python-bigquery/commit/30de15f7255de5ea221df4e8db7991d279e0ea28))

##### Dependencies

-   expand pyarrow dependencies to include version 2 ([#&#8203;368](https://www.github.com/googleapis/python-bigquery/issues/368)) ([cd9febd](https://www.github.com/googleapis/python-bigquery/commit/cd9febd20c34983781386c3bf603e5fca7135695))

</details>

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samples/snippets/requirements.txt

@@ -1,4 +1,4 @@
-google-cloud-bigquery==2.3.1
+google-cloud-bigquery==2.4.0
 google-cloud-bigquery-storage==2.0.1
 google-auth-oauthlib==0.4.2
 grpcio==1.33.2