[Fix] workday?, weekday? to return bool instead of true or nil

[3150]

Hello. I'm Brown.
It seems that workday?, weekday? return 'true' or 'nil' instead of false.

irb(main):009:0> RUBY_VERSION
=> "2.6.6"

irb(main):010:0> today = Date.current
=> Wed, 26 May 2021
irb(main):011:0> sunday = today + 3.days
=> Sat, 29 May 2021
irb(main):012:0> today.weekday?
=> true
irb(main):013:0> today.workday?
=> true

irb(main):015:0> sunday.weekday?
=> nil
irb(main):016:0> sunday.workday?
=> nil

It is because {SortedSet}.include?() returns true or nil

irb(main):020:0> BusinessTime::Config.weekdays
=> #<SortedSet: {1, 2, 3, 4, 5}>

irb(main):017:0> a = SortedSet.new([1,2])
=> #<SortedSet: {1, 2}>
irb(main):018:0> a.include?(2)
=> true
irb(main):019:0> a.include?(3)
=> nil

How about changing these two methods to return true or false like this?

irb(main):003:0> today = Date.current
=> Wed, 26 May 2021
irb(main):004:0> sunday = today + 3.days
=> Sat, 29 May 2021
irb(main):005:0> today.weekday?
=> true
irb(main):006:0> today.workday?
=> true
irb(main):007:0> sunday.weekday?
=> false
irb(main):008:0> sunday.workday?
=> false

related issue:
knu/sorted_set#2

[pmcnano]

Pushed a PR 🤞 knu/sorted_set#9

[rmm5t]

Thank you for this, but this is not necessary. If sorted_set wants to handle it, great, but it's not appropriate to handle here.