Add assets (drum sounds) for music extension

webpack.config.js

@@ -60,7 +60,13 @@ module.exports = [
             libraryTarget: 'commonjs2',
             path: path.resolve(__dirname, 'dist/node'),
             filename: '[name].js'
-        }
+        },
+        plugins: base.plugins.concat([
+            new CopyWebpackPlugin([{
+                from: './src/extensions/scratch3_music/assets',
+                to: 'assets/scratch3_music'
+            }])
+        ])
     }),
     // Playground
     defaultsDeep({}, base, {