Fix IMPORTANT block for deserialization in Docs

The IMPORTANT block must be wrapped with `====`

**Cherry-pick to 1.5.x**

src/reference/asciidoc/amqp.adoc

@@ -63,7 +63,7 @@ By default, only `java.util` and `java.lang` classes are deserialized.
 To revert to the previous behavior, you can add allowable class/package patterns by invoking `Message.addWhiteListPatterns(...)`.
 A simple `*` wildcard is supported, for example `com.foo.*, *.MyClass`.
 Bodies that cannot be deserialized will be represented by `byte[<size>]` in log messages.
-----
+====
 
 ===== Exchange