Update cacert.pem to latest version (2020-01-01)

[patmead]

File sourced from https://curl.haxx.se/docs/caextract.html

Fixes #384

[patmead]

This update does cause an error in the PHP 5.3 test script, but I hope that's an acceptable compromise given that:

• PHP 5.3 officially reached end-of-life in 2014, and
• PHP 5.3 users may still work around that issue by specifying a different ca-bundle as outlined in this project's documentation

(As an aside, that same document claims that "HTTPS requests will use the most secure options available" so hopefully this PR will bring us in line with that ;) )

[ozh]

Tests are flaky and easily timeout. I've triggered the build again and 5.3 pass, so I assume everything is fine with your PR

[ozh]

@rmccue we would really need you to ease the check status requirement to allow merging in such a situation

[patmead]

@rmccue Could you hit the Merge button on this approved PR? If there's anything blocking this from being merged please let me know!

[jrfnl]

The previous PRs for this - #212, #330 and #333 - contained discussion about adjustments made to the certificate for compatibility. I'm not sure those adjustments were made in this PR which has now been merged. It might be a good idea for someone who involved to have a critical look if another update is needed to this before a release.