lib/path.js
function diff(rootpath, src) {
  return _.isString(rootpath) && _.isString(src) ?
    src.replace(rootpath, '').split(path.sep).join('/') : ''
}
function diff(rootpath, src) {
  return _.isString(rootpath) && _.isString(src) ?
    src.replace(rootpath, '').split(path.sep).join('/') : ''
}
returns forward-slashed rel path (only use for better visual logging)