Update ex-rev.adoc

[CodeFerriCode]

Add V in revnumber to make it consistent with: (asciidoctor.org/docs/_includes/revision.adoc)

• In the converted document, notice that the V preceding the revnumber is capitalized in the byline but not when the attribute is referenced in the body of the document.
• When explicitly set, any characters preceding the version number are not dropped.

[mojavelinux]

A similar change was made to the new docs site. See https://docs.asciidoctor.org/asciidoc/latest/document/reference-revision-attributes/