[request] SHA256 checksum at TLS cert trust

[matineeschwarz]

Recommendation is to avoid SHA1, when SHA256 can be used. I understand it's complex to spoof it. Better to make it more secure anyway.

[sjaeckel]

Can you please check out whether PR #2080 solves the issue?

Btw. after implementing it, I realized that the only thing where it really mattered was whether we add the cert (a second time) to $XDG_DATA_HOME/profanity/certs/CAfile.pem or not. The hash is used nowhere else and the entire verification was done via having the cert in the CAfile and handing that one to the TLS stack.