Unpin cairo version in setup.py

[johnthagen]

This line:

pcb-tools/setup.py

Line 43 in cf4a612

'install_requires': ['cairocffi==0.6'],

Pins cairocffi at 0.6.0, but the latest is 1.1.0: https://pypi.org/project/cairocffi/

This means that Python applications that use pcb-tools are stuck with an older version. Is there a specific reason for pinning this to a 6 year old version?

[johnthagen]

This is also currently pinned in requirements.txt as well:

pcb-tools/requirements.txt

Line 2 in cf4a612

cairocffi==0.6