Update script-fields.asciidoc

> Script fields can work on fields that are not stored (`my_field_name` in
the above case), and allow to return custom values to be returned (the
evaluated value of the script).

Not sure what `my_field_name` is pointing to in the above example?

Author: louisong

docs/reference/search/request/script-fields.asciidoc

@@ -33,7 +33,7 @@ GET /_search
 // CONSOLE
 // TEST[setup:sales]
 
-Script fields can work on fields that are not stored (`test1` `test2` in
+Script fields can work on fields that are not stored (`my_field_name` in
 the above case), and allow to return custom values to be returned (the
 evaluated value of the script).