Minor fix in reference docs for BatchMapping methods

Closes gh-360

Author: rstoyanchev

spring-graphql-docs/src/docs/asciidoc/index.adoc

@@ -1569,7 +1569,7 @@ Batch mapping methods can return:
 | A sequence of batch loaded objects that must be in the same order as the source/parent
   objects passed into the method.
 
-| `Map<K,V>`, `List<V>`
+| `Map<K,V>`, `Collection<V>`
 | Imperative variants, e.g. without remote calls to make.
 
 |===