Fixed isOpen

The MDC dialog component doesn't have a method named "isOpen()", it's actually a property.

Author: TheBosZ

packages/dialog/Dialog.svelte

@@ -56,10 +56,10 @@
   }
 
   export function isOpen(...args) {
-    return dialog.isOpen(...args);
+    return dialog.isOpen;
   }
 
   export function layout(...args) {
     return dialog.layout(...args);
   }
-</script>
+</script>