function errorDiff(err, type, escape) {
  var actual = escape ? escapeInvisibles(err.actual) : err.actual;
  var expected = escape ? escapeInvisibles(err.expected) : err.expected;
  return diff['diff' + type](actual, expected).map(function(str) {
    if (str.added) {
      return colorLines('diff added', str.value);
    }
    if (str.removed) {
      return colorLines('diff removed', str.value);
    }
    return str.value;
  }).join('');
}
Return a character diff for `err`.

@api private
@param {Error} err
@param {string} type
@param {boolean} escape
@return {string}