There is an ongoing outage on the primary CPAN mirror. It is possible to work around the issue by using MetaCPAN as a mirror.
update
$0 [--minor|--major]
Module Install Instructions
To install pantheon, copy and paste the appropriate command in to your terminal.
cpanm pantheon
perl -MCPAN -e shell
install pantheon
For more information on module installation, please visit the detailed CPAN module installation guide.