drop require 'rubygems', it is not required in pkgsrc and not in ruby18-base.
Update ruby-spreadsheet to 0.9.0.

### 0.9.0 / 16.09.2013

* Author: Pavel <pavel.evst@gmail.com>
Date:   Mon Sep 16 14:02:49 2013 +0700

* Test cases for Worksheet#margins, Worksheet#pagesetup, Workbook#delete_worksheet. Fix bugs related to it.
* Page margins reader/writter
* Markdownify GUIDE
* Add page setup options (landscape or portrait and adjust_to)
Updated math/ruby-spreadsheet to 0.9.0