code: function stringDiff(existing, proposed, method) {
    method = method || 'diffJson';
    lazy.diff[method](existing, proposed).forEach(function (res) {
      var color = utils.gray;
      if (res.added) color = utils.green;
      if (res.removed) color = utils.red;
      process.stdout.write(color(res.value));
    });
    console.log('\n');
  }
docs: Show a diff comparison of the existing content versus the content
  about to be written.
  
  @param  {String} `existing`
  @param  {String} `proposed`
  @param  {String} method Optionally pass a specific method name from the [diff] library to use for the diff.
  @return {String} Visual diff comparison.