small edit in plotmap()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/bayesr@1027 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
small edit in plotmap()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/bayesr@1028 edb9625f-4e0d-4859-8d74-9fd3b1da38cb