The current default.pem file in Arcanist is from `Wed Jan 20 04:12:04 2016` and at this point is out of date
This revision replaces that `.pem` file with the one from here `https://curl.se/ca/cacert.pem` which is the Mozilla CA Certificate store from https://curl.se/docs/caextract.html
Specifically, this addresses any issues with the LetsEncrypt root certificate expiration of `9/30/21`