Changes:

• Update Drupal8 to latest upstream version - 8.7.1. Resolves:
  • SA-CORE-2019-006 - Moderately critical security issue(s).
  • SA-CORE-2019-007 - Moderately critical security issue(s).
• Fix broken cron job - closes #1317. [ Stefan Davis ]
• Include additional php packages (uploadprogress and mbstring) to improve user experience.
• Update readme to include notes regarding composer update; plus new links to docs.

Links

• Release meta-files (signature, manifest)