Add compatibility for Ruby 3.0 #190
                
     Merged
            
            
          
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This addresses two issues where method calls needed to be updated due to changes in Ruby 3.0 argument passing. I also updated the CI configuration to add Ruby 3 and newer bugfix builds of Ruby/Rails, but happy to revert those changes if needed. I also added sassc-rails to the Gemfile, as development/testing doesn't work out of the box without it.
Fixes #189