Need an expired self-signed certificate to run tests on CI

[nathany]

I have valid and expired certificates, but I don't want to include them in the open source project for obvious reasons.

There may be a way to store them on CI, or perhaps some level of mocking instead of full integration tests.

https://docs.travis-ci.com/user/encrypting-files/

[nathany]

I've added a self-signed *.p12 cert for testing in #19. Still need a self-signed expired cert as well. Though I tried creating a cert that expires in one day, that didn't work for some reason.