Comment 2 for bug 1620755

Same problem here

error: cannot perform the following tasks:
- Download snap "ubuntu-core" from channel "stable" (Get https://search.apps.ubuntu.com/api/v1/search?fields=anon_download_url%2Carchitecture%2Cchannel%2Cdownload_sha512%2Csummary%2Cdescription%2Cbinary_filesize%2Cdownload_url%2Cicon_url%2Clast_updated%2Cpackage_name%2Cprices%2Cpublisher%2Cratings_average%2Crevision%2Csnap_id%2Csupport_url%2Ctitle%2Ccontent%2Cversion%2Corigin%2Cprivate%2Cconfinement&q=package_name%3A%22ubuntu-core%22: x509: certificate signed by unknown authority)