chore(deps): update dependency pillow to v6.2.2 [(#3186)](GoogleCloudPlatform/python-docs-samples#3186)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [pillow](https://python-pillow.org) ([source](https://github.com/python-pillow/Pillow)) | patch | `==6.2.1` -> `==6.2.2` |

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### Release Notes

<details>
<summary>python-pillow/Pillow</summary>

### [`v6.2.2`](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst#&#8203;622-2020-01-02)

[Compare Source](https://github.com/python-pillow/Pillow/compare/6.2.1...6.2.2)

-   This is the last Pillow release to support Python 2.7 [#&#8203;3642](https://github.com/python-pillow/Pillow/issues/3642)

-   Overflow checks for realloc for tiff decoding. CVE-2020-5310
    [wiredfool, radarhere]

-   Catch SGI buffer overrun. CVE-2020-5311
    [radarhere]

-   Catch PCX P mode buffer overrun. CVE-2020-5312
    [radarhere]

-   Catch FLI buffer overrun. CVE-2020-5313
    [radarhere]

-   Raise an error for an invalid number of bands in FPX image. CVE-2019-19911
    [wiredfool, radarhere]

</details>

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samples/snippets/crop_hints/requirements.txt

@@ -1,2 +1,2 @@
 google-cloud-vision==0.42.0
-pillow==6.2.1
+pillow==6.2.2

samples/snippets/document_text/requirements.txt

@@ -1,2 +1,2 @@
 google-cloud-vision==0.42.0
-pillow==6.2.1
+pillow==6.2.2

samples/snippets/face_detection/requirements.txt

@@ -1,2 +1,2 @@
 google-cloud-vision==0.42.0
-pillow==6.2.1
+pillow==6.2.2