Modification to allow installation on spree_core 1.3

commented out "s.add_dependency 'spree', '~> 1.2.0'" from spree_reuse_credit_card.gemspec 

installation will work on 1.3 after that line is commented out. from my brief testing, the extension does work in 1.3 and payment provider (stripe) did accept my customer_token for the charge. verified the charge in my stripe customer dashboard as well.