Remove jruby support pending later investigation

Getting this error message. It appears to have something to do with DateTime or Date.

Nacre::Order.get should make a request to the correct endpoint
     Failure/Error: resource = described_class.get(range)
     NoMethodError:
       undefined method `/' for "000":String
     # ./lib/nacre/order/invoice.rb:15:in `tax_date='
     # ./lib/nacre/abstract_resource.rb:30:in `attributes='
     # ./lib/nacre/abstract_resource.rb:28:in `attributes='
     # ./lib/nacre/abstract_resource.rb:24:in `initialize'
     # ./lib/nacre/order/invoice_collection.rb:11:in `initialize'
     # ./lib/nacre/order/invoice_collection.rb:10:in `initialize'
     # ./lib/nacre/order.rb:40:in `invoices='
     # ./lib/nacre/abstract_resource.rb:30:in `attributes='
     # ./lib/nacre/abstract_resource.rb:28:in `attributes='
     # ./lib/nacre/abstract_resource.rb:24:in `initialize'
     # ./lib/nacre/abstract_resource.rb:37:in `from_json'
     # ./lib/nacre/abstract_resource.rb:43:in `get'
     # ./spec/lib/nacre/order_spec.rb:185:in `(root)'