chore(deps): update dependency google-cloud-storage to v1.31.2 (#50)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [google-cloud-storage](https://togithub.com/googleapis/python-storage) | patch | `==1.31.0` -> `==1.31.2` |

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### Release Notes

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

### [`v1.31.2`](https://togithub.com/googleapis/python-storage/blob/master/CHANGELOG.md#&#8203;1312-httpswwwgithubcomgoogleapispython-storagecomparev1311v1312-2020-09-23)

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

### [`v1.31.1`](https://togithub.com/googleapis/python-storage/blob/master/CHANGELOG.md#&#8203;1311-httpswwwgithubcomgoogleapispython-storagecomparev1310v1311-2020-09-16)

[Compare Source](https://togithub.com/googleapis/python-storage/compare/v1.31.0...v1.31.1)

</details>

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samples/snippets/detect/requirements.txt

@@ -1,2 +1,2 @@
 google-cloud-vision==2.0.0
-google-cloud-storage==1.31.0
+google-cloud-storage==1.31.2

samples/snippets/product_search/requirements.txt

@@ -1,2 +1,2 @@
 google-cloud-vision==2.0.0
-google-cloud-storage==1.31.0
+google-cloud-storage==1.31.2