Followup to r1479563, fix typos in documentation.

* subversion/bindings/swig/perl/native/Core.pm
  (svn_opt_revision_t): s/$VN/$SVN/


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1487083 13f79535-47bb-0310-9956-ffa450edef68