Fix `DEPRECATION WARNING: TimeWithZone#to_s(:short)`

[iainbeeston]

Rails has deprecated passing a parameter to to_s and now expects to_formatted_s to be used instead.

This is the full error I see:

DEPRECATION WARNING: TimeWithZone#to_s(:short) is deprecated. Please use TimeWithZone#to_fs(:short) instead. (called from to_s at /ice-cube-ruby/ice_cube/lib/ice_cube/occurrence.rb:89)

[adfoster-r7]

Looks like this is now an error in newer versions of Active Support:

Failures:

  1) IceCube::Occurrence to_s accepts a format option to comply with ActiveSupport
     Failure/Error: expect(occurrence.to_s(:short)).to eq time_now.to_s(:short)
     
     ArgumentError:
       wrong number of arguments (given 1, expected 0)
     # /Users/user/.rvm/gems/ruby-3.0.2@pro/gems/activesupport-7.1.3/lib/active_support/time_with_zone.rb:200:in `to_s'
     # ./spec/examples/occurrence_spec.rb:31:in `block (3 levels) in <top (required)>'
     # ./spec/spec_helper.rb:76:in `block (3 levels) in <top (required)>'
     # ./spec/spec_helper.rb:75:in `block (2 levels) in <top (required)>'

After applying these changes locally, they pass though :+1: