old_contents: var whitespace = require('../regex/whitespace')
  
  function isWhiteSpace (str) {
    return whitespace().test(str)
  }
  
  module.exports = isWhiteSpace
  
new_contents: var whitespace = require('./rex-whitespace')
  var contains = require('./contains')
  
  function isWhiteSpace (str) {
    return contains(whitespace(), str)
  }
  
  module.exports = isWhiteSpace
  
subject: update regex/isWhiteSpace.js