Fix VM memory allocation optimizations by reducing what we allocate on the heap

internal/builtins/join.go

@@ -17,10 +17,10 @@ func Join(args ...object.Object) object.Object {
 	}
 
 	arr := args[0].(*object.Array)
-	sep := args[1].(*object.String)
+	sep := args[1].(object.String)
 	a := make([]string, len(arr.Elements))
 	for i, el := range arr.Elements {
 		a[i] = el.String()
 	}
-	return &object.String{Value: strings.Join(a, sep.Value)}
+	return object.String{Value: strings.Join(a, sep.Value)}
 }