Merge pull request urvin-compliance#108 from AliceVerner:fix_cols

Fix cols method in table_model

lib/caracal/core/models/table_model.rb

@@ -61,7 +61,7 @@ def cells
         end
 
         def cols
-          rows.reduce([]) do |array, row|
+          @cols ||= rows.reduce([]) do |array, row|
             row.each_with_index do |cell, index|
               array[index]  = []    if array[index].nil?
               array[index] << cell