Summary
Changed Docker base to Centos6.9 in order to support older Linux distributions.
Primary suggestion came from https://docs.appimage.org/packaging-guide/other-resources/ingredients.html#binaries-compiled-on-old-enough-base-system
Bug Fixes
- AppImage now run on CentOS/Fedora/Redhat distributions newer than CentOS6.9, as well as Debian based distros above 7 (Wheezy).