#425 - Fix lack of @Modifying in reference documentation code.

Author: okue

src/main/asciidoc/reference/r2dbc-repositories.adoc

@@ -260,6 +260,7 @@ As this approach is feasible for comprehensive custom functionality, you can mod
 ====
 [source,java]
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+@Modifying
 @Query("UPDATE person SET firstname = :firstname where lastname = :lastname")
 Mono<Integer> setFixedFirstnameFor(String firstname, String lastname);
 ----