Rakefile in ruby-dnn-1.2.2 vs Rakefile in ruby-dnn-1.2.3

@@ -1,14 +1,19 @@
 require "bundler/gem_tasks"
 require "rake/testtask"
+require "rake/extensiontask"
 require "yard"
 require "yard/rake/yardoc_task"
 
 Rake::TestTask.new(:test) do |t|
   t.libs << "test"
   t.libs << "ext"
   t.libs << "lib"
   t.test_files = FileList["test/*_test.rb", "test/layers_test/*_test.rb"]
+end
+
+Rake::ExtensionTask.new "rb_stb_image" do |ext|
+  ext.lib_dir = "lib/rb_stb_image"
 end
 
 task :build_rb_stb_image do
   sh "cd ext/rb_stb_image; ruby extconf.rb; make"
 end