Allow passing in the Stripe API version as an initialiation option

lib/active_merchant/billing/gateways/stripe.rb

@@ -33,6 +33,8 @@ def initialize(options = {})
         requires!(options, :login)
         @api_key = options[:login]
         @fee_refund_api_key = options[:fee_refund_login]
+        @version = options[:version]
+
         super
       end
 
@@ -258,15 +260,16 @@ def headers(options = {})
           :publisher => 'active_merchant'
         })
 
-        key = options[:key] || @api_key
+        key     = options[:key] || @api_key
+        version = options[:version] || @version
 
         headers = {
           "Authorization" => "Basic " + Base64.encode64(key.to_s + ":").strip,
           "User-Agent" => "Stripe/v1 ActiveMerchantBindings/#{ActiveMerchant::VERSION}",
           "X-Stripe-Client-User-Agent" => @@ua,
           "X-Stripe-Client-User-Metadata" => {:ip => options[:ip]}.to_json
         }
-        headers.merge!("Stripe-Version" => options[:version]) if options[:version]
+        headers.merge!("Stripe-Version" => version) if version
         headers
       end
 

test/unit/gateways/stripe_test.rb

@@ -316,6 +316,15 @@ def test_optional_version_header
     @gateway.purchase(@amount, @credit_card, @options.merge(:version => '2013-10-29'))
   end
 
+  def test_initialize_gateway_with_version
+    @gateway = StripeGateway.new(:login => 'login', :version => '2013-12-03')
+    @gateway.expects(:ssl_request).once.with {|method, url, post, headers|
+      headers && headers['Stripe-Version'] == '2013-12-03'
+    }.returns(successful_purchase_response)
+
+    @gateway.purchase(@amount, @credit_card, @options)
+  end
+
   def test_track_data_and_traditional_should_be_mutually_exclusive
     stub_comms(@gateway, :ssl_request) do
       @gateway.purchase(@amount, @credit_card, @options)