This evening I attempted to set up a 1.14.2 dev environment on my Ubuntu 18.04 LTS box. It's a pretty new installation, so I have been installing things here and there as I need them. Strangely enough, when I attempt to cURL the mdk file, cURL refuses to validate the certificate for files.minecraftforge.net.
> curl https://files.minecraftforge.net/
curl: (60) SSL certificate problem: unable to get local issuer certificate
More details here: https://curl.haxx.se/docs/sslcerts.html
Firefox doesn't have a problem with the certificate, but I can see that it was just issued today (June 11, 2019). I'm not sure if this is just an issue of time zones or something more significant. OpenSSL also refuses to verify the certificate if I export it out of Firefox. However, the main certificate for minecraftforge.net does validate and it has the same root cert as files.minecraftforge.net, so it's probably an issue that will resolve itself.
If it's a matter of timezones, then this topic is not a real issue. However, I see there are three or four topics recently that have this issue at their root and I wanted to document my findings here.
Cheers!
-jadar