Ubuntu upstream packages use expired certificate

I was trying to debug a kernel issue on a client's Ubuntu machine and needed a newer bcc according to #2119. Unfortunately, there is an expired certificate issue preventing the upstream packaging from being installed:

```
$ sudo apt-get update
Hit:1 http:// InRelease
Hit:2 http:///mirror/archive.ubuntu.com/ubuntu bionic InRelease
Hit:3 http:///mirror/archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit:4 http:///mirror/archive.ubuntu.com/ubuntu bionic-backports InRelease
Hit:5 http:///mirror/archive.ubuntu.com/ubuntu bionic-security InRelease
Ign:6 https://repo.iovisor.org/apt/bionic bionic InRelease
Err:7 https://repo.iovisor.org/apt/bionic bionic Release
Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate. Could not handshake: Error in the certificate verification. [IP: 104.199.116.191 443]
Reading package lists... Done
E: The repository 'https://repo.iovisor.org/apt/bionic bionic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
```

Both Upstream Stable and Upstream Nightly packages are broken by this.

Start by checking the Upstream Stable and Upstream Nightly repository configuration and the certificate chain reported by apt-get update. Confirm the issue is resolved when both bionic repositories update securely without the expired-certificate error.

Written by the indexing model from the issue text.