Bump pillow from 7.2.0 to 8.1.1 (#13)

Bumps [pillow](https://github.com/python-pillow/Pillow) from 7.2.0 to 8.1.1.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@7.2.0...8.1.1)

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Author: dependabot[bot]

poetry.lock

@@ -16,7 +16,7 @@ classifiers = [
 [tool.poetry.dependencies]
 python = "^3.6"
 requests = "^2.24.0"
-pillow = "^7.2.0"
+pillow = ">=7.2,<9.0"
 numpy = "^1.16"
 dataclasses = { version = "^0.7", python = ">=3.6,<3.7" }