PR: https://github.com/mongodb/mongoid/pull/5760

This PR does not alter the compatibility contents (e.g. which versions support what), it merely cleans up the format:

• Combine columns which have same values, e.g. with header "7.2 thru 7.5"
• Remove mention of version 6.4 which is super old at this point
• In Ruby Compatibility table, flip-flop JRuby 9.3 and 9.2 cols so that higher comes first, to keep ordering consistent with rest of tables