Update webpack.config.js global object fix

`this` might be okay, I'm not actually sure, but xterm.js uses `globalThis` and so I think consistency is better maybe?

addons/addon-serialize/webpack.config.js

@@ -34,7 +34,8 @@ module.exports = {
     path: path.resolve('./lib'),
     library: addonName,
     libraryTarget: 'umd',
-    globalObject: 'this'
+    // Force usage of globalThis instead of global / self. (This is cross-env compatible)
+    globalObject: 'globalThis',
   },
   mode: 'production'
 };