update gemspec
update gemspec

StemboltHQ/spree-payment-method-fee,freerunningtech/spree-payment-method-fee,ikazoy/spree-payment-method-fee,degica/spree-payment-method-fee,shioyama/spree-payment-method-fee,StemboltHQ/spree-payment-method-fee,degica/spree-payment-method-fee,shioyama/spree-payment-method-fee,ikazoy/spree-payment-method-fee,shioyama/spree-payment-method-fee,freerunningtech/spree-payment-method-fee,degica/spree-payment-method-fee,ikazoy/spree-payment-method-fee