code: function digits(val, num, ch) {
    return pad(val, num - val.length, ch);
  }
docs: Left pad the given `value` with the specified `number` of zeros
  or alternate `character`.
  
  ```js
  digits('abc', 10);
  //=> '0000000000abc'
  
  digits('abc', 10, '~');
  //=> '~~~~~~~~~~abc'
  ```
  
  @param {String} `value`
  @param {String} `number`
  @return {String} `character`
  @api public