Main page only list draft 3 and 4 being supported while draft6 was added as well.

See https://github.com/jsonrainbow/json-schema/pull/835 where draft 6 support was added. The definition on https://bowtie.report/#/implementations/php-justinrainbow-json-schema also lists draft 6 already and so should our main page.