Revert "Bump Python version to 3.9"

This reverts commit 46466de7db.

Tox wasn't set up correctly for this bump, and we may want to keep
compatibility with older Blenders as well.

pyproject.toml

@@ -21,7 +21,7 @@ classifiers = [
 s3 = ["boto3"]
 
 [tool.poetry.dependencies]
-python = "^3.9"
+python = "^3.5"
 requests = "^2.11"
 
 # For S3 storage support:
@@ -42,7 +42,6 @@ sphinx-rtd-theme = "^0.4"
 responses = "^0.10"
 pathlib2 = {version = "^2.3", python = "<3.6"}
 tox = "^3.12"
-types-requests = "^2.25.0"
 
 [tool.poetry.scripts]
 bat = 'blender_asset_tracer.cli:cli_main'