fix: change globalObject to globalThis (#579)

In ESM `this` is undefined at the top level. Instead to access the global object you must use `globalThis`.

Co-authored-by: Kagami Sascha Rosylight <[email protected]>

Author: lucacasonato

Diff for: webpack.config.cjs

@@ -7,7 +7,7 @@ module.exports = {
     path: path.resolve(__dirname, "dist"),
     library: "WebIDL2",
     libraryTarget: "umd",
-    globalObject: "this"
+    globalObject: "globalThis"
   },
   mode: "production",
   devtool: "source-map",