Default the built-in Jenkins Update Center URL to https://updates.jenkins.io instead of obsolete HTTP endpoint. This requires a JRE compatible with Let's ...

... <url> <loc>https://www.jenkins.io/2.0/</loc> ... blog/2010/02/02/welcome-to-continuous-blog/</loc> ... plugins/</loc> <lastmod>2010-02-12</lastmod> <priority>0.5 ...