chore(deps): update dependency google-cloud-storage to v1.31.0 (#77)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [google-cloud-storage](https://github.com/googleapis/python-storage) | minor | `==1.30.0` -> `==1.31.0` |

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### Release Notes

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

### [`v1.31.0`](https://github.com/googleapis/python-storage/blob/master/CHANGELOG.md#&#8203;1310-httpswwwgithubcomgoogleapispython-storagecomparev1300v1310-2020-08-26)

[Compare Source](https://github.com/googleapis/python-storage/compare/v1.30.0...v1.31.0)

##### Features

-   add configurable checksumming for blob uploads and downloads ([#&#8203;246](https://www.github.com/googleapis/python-storage/issues/246)) ([23b7d1c](https://www.github.com/googleapis/python-storage/commit/23b7d1c3155deae3c804c510dee3a7cec97cd46c))
-   add support for 'Blob.custom_time' and lifecycle rules ([#&#8203;199](https://www.github.com/googleapis/python-storage/issues/199)) ([180873d](https://www.github.com/googleapis/python-storage/commit/180873de139f7f8e00b7bef423bc15760cf68cc2))
-   error message return from api ([#&#8203;235](https://www.github.com/googleapis/python-storage/issues/235)) ([a8de586](https://www.github.com/googleapis/python-storage/commit/a8de5868f32b45868f178f420138fcd2fe42f5fd))
-   **storage:** add support of daysSinceNoncurrentTime and noncurrentTimeBefore ([#&#8203;162](https://www.github.com/googleapis/python-storage/issues/162)) ([136c097](https://www.github.com/googleapis/python-storage/commit/136c0970f8ef7ad4751104e3b8b7dd3204220a67))
-   pass 'client_options' to base class ctor ([#&#8203;225](https://www.github.com/googleapis/python-storage/issues/225)) ([e1f91fc](https://www.github.com/googleapis/python-storage/commit/e1f91fcca6c001bc3b0c5f759a7a003fcf60c0a6)), closes [#&#8203;210](https://www.github.com/googleapis/python-storage/issues/210)
-   rename 'Blob.download_as_{string,bytes}', add 'Blob.download_as_text' ([#&#8203;182](https://www.github.com/googleapis/python-storage/issues/182)) ([73107c3](https://www.github.com/googleapis/python-storage/commit/73107c35f23c4a358e957c2b8188300a7fa958fe))

##### Bug Fixes

-   change datetime.now to utcnow ([#&#8203;251](https://www.github.com/googleapis/python-storage/issues/251)) ([3465d08](https://www.github.com/googleapis/python-storage/commit/3465d08e098edb250dee5e97d1fb9ded8bae5700)), closes [#&#8203;228](https://www.github.com/googleapis/python-storage/issues/228)
-   extract hashes correctly during download ([#&#8203;238](https://www.github.com/googleapis/python-storage/issues/238)) ([23cfb65](https://www.github.com/googleapis/python-storage/commit/23cfb65c3a3b10759c67846e162e4ed77a3f5307))
-   repair mal-formed docstring ([#&#8203;255](https://www.github.com/googleapis/python-storage/issues/255)) ([e722376](https://www.github.com/googleapis/python-storage/commit/e722376371cb8a3acc46d6c84fb41f4e874f41aa))

##### Documentation

-   update docs build (via synth) ([#&#8203;222](https://www.github.com/googleapis/python-storage/issues/222)) ([4c5adfa](https://www.github.com/googleapis/python-storage/commit/4c5adfa6e05bf018d72ee1a7e99679fd55f2c662))

</details>

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samples/snippets/requirements.txt

@@ -1,4 +1,4 @@
-google-cloud-storage==1.30.0
+google-cloud-storage==1.31.0
 google-cloud-asset==2.0.0
 google-cloud-resource-manager==0.30.2
 google-cloud-pubsub==1.7.0