Also re-implement Charge#refund to use our new endpoint

This was already done for `ApplicationFee`.

lib/stripe/charge.rb

@@ -5,8 +5,12 @@ module Stripe
     include Stripe::APIOperations::Update
 
     def refund(params={}, opts={})
-      response, opts = request(:post, refund_url, params, opts)
-      initialize_from(response, opts)
+      self.refunds.create
+
+      # now that a refund has been created, we expect the state of this object
+      # to change as well (i.e. `refunded` will now be `true`) so refresh it
+      # from the server
+      self.refresh
     end
     extend Gem::Deprecate
     deprecate :refund, "charge.refunds.create", 2016, 07

test/stripe/application_fee_test.rb

@@ -28,7 +28,8 @@ module Stripe
       begin
         fee = Stripe::ApplicationFee.construct_from(make_application_fee)
 
-        # creates the refund
+        # creates the refund (this is not how the endpoint would actually
+        # respond, but we discard the result anyway)
         @mock.expects(:post).once.
           with("#{Stripe.api_base}/v1/application_fees/#{fee.id}/refunds", nil, '').
           returns(make_response({}))

test/stripe/charge_test.rb

@@ -120,9 +120,18 @@ module Stripe
       $stderr = StringIO.new
       begin
         charge = Stripe::Charge.construct_from(make_charge)
+
+        # creates the refund (this is not how the endpoint would actually
+        # respond, but we discard the result anyway)
         @mock.expects(:post).once.
-          with("#{Stripe.api_base}/v1/charges/#{charge.id}/refund", nil, '').
+          with("#{Stripe.api_base}/v1/charges/#{charge.id}/refunds", nil, '').
+          returns(make_response({}))
+
+        # reloads the charge to get the field updates
+        @mock.expects(:get).once.
+          with("#{Stripe.api_base}/v1/charges/#{charge.id}", nil, nil).
           returns(make_response({:id => charge.id, :refunded => true}))
+
         charge.refund
         message = "NOTE: Stripe::Charge#refund is deprecated; use " +
           "charge.refunds.create instead"