Omit author_email if @ not found in authors

[evandrocoan]

Following from: PyO3#289 - Stop passing author.email to python

Fixes deploying to PyPI when an email address is not provided.

This master branch also needs to be updated due the requirement:

File: anki/rspy/requirements.txt
1: # fixme: when maturin fixes 32 bit support, switch back to pypi
2: git+https://github.com/dae/maturin#egg=maturin; sys_platform == "linux" and platform_machine != "x86_64"
3: maturin; sys_platform != "linux" or platform_machine == "x86_64"

As of today, the new release 0.80.0 of maturin was released, within this fix, and it will be automatically used on the next installation because there is no restriction on the maturin requirement version.