Add setter for last_4_digits

Now that last_4_digits is not an attribute it will not have a
setter generated for it. This adds such a setter method.

Author: ugexe

lib/minfraud/components/credit_card.rb

@@ -74,7 +74,7 @@ class CreditCard < Base
       # @return [Boolean, nil]
       attr_accessor :was_3d_secure_successful
 
-      # The last digits of the credit card number.
+      # Get the last digits of the credit card number.
       #
       # @deprecated Use {::last_digits} instead.
       #
@@ -83,6 +83,15 @@ def last_4_digits
         @last_digits
       end
 
+      # Set the last digits of the credit card number.
+      #
+      # @deprecated Use {::last_digits} instead.
+      #
+      # @return [String, nil]
+      def last_4_digits=(last4)
+        @last_digits = last4
+      end
+
       # @param params [Hash] Hash of parameters. Each key/value should
       #   correspond to one of the available attributes.
       def initialize(params = {})