Revert "fix: invalid string type (#77)" (#80)

This reverts commit 13fc5ed.

Author: jerson

lib/web/rsa_web.dart

@@ -7,7 +7,9 @@ import 'package:web/web.dart';
 
 class FastRsaPlugin {
   var _counter = 0;
-  Worker worker = Worker('assets/packages/fast_rsa/web/assets/worker.js');
+  Worker worker = Worker(
+    'assets/packages/fast_rsa/web/assets/worker.js'.toJS,
+  );
   Map<String, Completer<Uint8List>> completers = {};
 
   static void registerWith(Registrar registrar) {