pypi metadata sets python 3.10 as a requirement

[Ray Plante]

I'm using json-spec with Python 3.8 and would like to the package to 0.11.0 (to get rid of collections.abc warnings; see also #26). Although the documentation (and the .travis file) indicate that Python versions as low as 3.6 are supported, the pypi metadata for the package places a requirement of 3.10. This prevents pip from upgrading the package.

It appears that the source of this metadata is the pyproject.toml file (at line 63):

[tool.poetry.dependencies]
python = "^3.10"

Is 3.10 truly required? If so, we can update the documentation, but hopefully just the pyproject.toml file can be updated to reduce this requirement.