Add dynamic = ["version"] to pyproject.toml

[jamestwebber]

This is a minor thing, but the pyproject.toml file generated by maturin init is not quite valid according to the schema (e.g. here). The [project] table should have an entry for version, or it should be a dynamic property.

Since maturin is automatically pulling the version from cargo.toml anyway, it's a simple fix to just add dynamic = ["version"] to the project table. This makes the toml follow the spec and the tool is already doing the right thing--no further config needed, as far as I can tell.