Check for updates to insecure gems

[petitJAM]

Sometimes a gem is insecure, but there is no security patch for it yet. This totally breaks our deployments because of scan_gems. There's a work around with I_KNOW_GEMS_ARE_INSECURE, but it's a huge pain.

I propose that the scan_gems task pings rubygems.org to find the latest version of the insecure gem to see if there's an update. If there is no update, it should not stop the deployment process and instead just display a warning. If there is an update, it should abort the deployment as it does now.

The task in question:

jefferies_tube/lib/jefferies_tube/capistrano/deploy.rb

Line 26 in 06cb6c8

task :scan_gems do

[petitJAM]

That PR got merged, but I've reverted it before release. The concern is that a gem like omniauth which was insecure with no patch but had mitigations could hide behind this without being noticed.

Slack discussion here:
https://tenforward.slack.com/archives/C02TQ688M/p1613766588144900