use trustme instead of hardcoded certificates

[moisesguimaraes]

https://pypi.org/project/trustme/

https://github.com/cherrypy/cheroot/blob/bee5df9/cheroot/test/test_ssl.py#L123-L154

https://github.com/aio-libs/aiohttp/blob/8a9dbf9/tests/conftest.py#L34-L84