Release 0.3.1

• Fix Drop not exiting immediately after the sandboxed process
  terminated, but waiting until its stdin was closed.
• Fix drop update --check reporting that a new version is available
  when the installed version is already up to date.
• Report an actionable error when Drop is run on Ubuntu without an
  AppArmor profile that allows creating user namespaces. The error was
  previously reported as fork/exec /proc/self/exe: permission denied,
  now it points to the missing capabilities:
  https://droprun.sh/docs/installation/#ubuntu-24---apparmor-config
• Update to Go compiler version 1.27.2