Insert current date in Google Spreadsheets

// Insert current date in Google Spreadsheet
function onOpen() {
  var ui = SpreadsheetApp.getUi();
  // Or FormApp or SpreadsheetApp.
  ui.createMenu('Custom Menu')
      .addItem('Insert Date', 'insertDate')
      .addToUi();

}

function insertDate() {
  var cell = SpreadsheetApp.getActive().getActiveCell();
  if (cell) {
      var d = new Date();
      var dd = d.getDate();
      dd = pad(dd, 2)
      var mm = d.getMonth() + 1; //Months are zero based
      mm = pad(mm, 2)
      var yyyy = d.getFullYear();
      var date = dd + "-" + mm + "-" + yyyy;
      var element = cell.setValue(date);
    } else {
      SpreadsheetApp.getUi().alert('Cannot get active cell.');
  }

}
function pad (str, max) {
  str = str.toString();
  return str.length < max ? pad("0" + str, max) : str;
}

complete novice to scripting... when I run this script I get an error for the pad function:

TypeError: Cannot call method "toString" of undefined. (line 28, file "Code")D

I forked this and created a simpler version that uses the built in date formatting:
https://gist.github.com/chrisbennell/65f9fb82f677c3a5c436c9535b268dbd