Fix HTTP interface section title in ref docs

src/docs/asciidoc/integration.adoc

@@ -364,7 +364,7 @@ If necessary the `Content-Type` may also be set explicitly.
 
 
 [[rest-http-interface]]
-  === HTTP Interface
+=== HTTP Interface
 
 The Spring Framework lets you define an HTTP service as a Java interface with annotated
 methods for HTTP exchanges. You can then generate a proxy that implements this interface