function rebase(root, src, dest) {
  let relp = rel(root, src)
  return relp ? path.join(dest, relp) : ''
}
function rebase(root, src, dest) {
  let relp = rel(root, src)
  return relp ? path.join(dest, relp) : ''
}
function rebase ( root , src , dest ) { let relp = rel ( root , src ) return relp ? path . join ( dest , relp ) : '' }
returns rel appended to dest root
returns rel appended to dest root