Fix double main invocation using shim mode (#295)

* Use shim mode to prevent double main invocation

* Update changelog

Author: JordanMartinez

CHANGELOG.md

@@ -9,6 +9,7 @@ Breaking changes:
 New features:
 
 Bugfixes:
+- Fix double `main` invocation (#295 by @JordanMartinez)
 
 Other improvements:
 

client/public/frame.html

@@ -7,13 +7,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <script>
     window.esmsInitOptions = {
-      // -- Hooks --
-      // Module load error
-      onerror: (e) => {
-        console.log("Error while loading module: ");
-        console.log(e);
-        throw e;
-      },
+      shimMode: true,
     };
   </script>
   <!--