v0.12.0

• Update build matrix for ActiveSupport 7 support ([#215])
• Remove dependency on sorted_set and rbtree ([#214])

Both BusinessTime::Config.holidays and BusinessTime::Config.weekdays now
return a Set instead of a SortedSet.

Warning: BusinessTime::Config.holidays no longer keeps holidays in sorted
order. If you rely on holidays returning in sorted order, please be sure to
load them in sorted order.