title: Modifying spreadsheet gem (Ruby)
body: <p>I have an excel file "stores.xls" with one worksheet, two columns and 10 rows.
  I am trying to edit the second column with Spreadsheet gem in Ruby, and I don't get any error during the process, but when I try to open the file I get "format is not valid" and sometimes "block in biff_version. Unknown BIFF version".</p>
  
  <p>Any ideas?</p>
  
  <pre><code>require 'spreadsheet'
  
  book = Spreadsheet.open 'stores.xls'
  sheet = book.worksheet 0 
  
  sheet.each do |row|
      nameStore = row[0]
      source = nameStore + ".com"
      row[1] = source
  end
  
  book.write 'stores.xls'
  </code></pre>