Merge pull request #57 from aai-institute/cleanup/python-3-9

Cleanup: Require Python 3.9.

pyproject.toml

@@ -8,7 +8,7 @@ description = "Learning function operators with neural networks."
 authors = [{ name = "Samuel Burbulla", email = "[email protected]" }]
 license = { file = "LICENSE.txt" }
 readme = "README.md"
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 classifiers = [
     "Development Status :: 3 - Alpha",
     "Programming Language :: Python",