Monkey patch GD2::AnimatedGif to fix the finalizer

https://github.com/dark-panda/gd2-ffij/pull/27

config/initializers/gd2.rb

@@ -0,0 +1,15 @@
+module OpenStreetMap
+  module GD2
+    module AnimatedGif
+      def frames_finalizer
+        proc do
+          @frames.each do |frame|
+            ::GD2::GD2FFI.send(:gdFree, frame.ptr)
+          end
+        end
+      end
+    end
+  end
+end
+
+GD2::AnimatedGif.prepend(OpenStreetMap::GD2::AnimatedGif)