[gnome-sudoku] Revert unrelated change in previous commit

[Michael Catanzaro <mcatanzaro src gnome org>]

commit fa4a06a1c0cede8d18a8383739cb74e7323035b6
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Sat Oct 4 16:44:14 2014 -0500

    Revert unrelated change in previous commit
    
    Whoops

 lib/sudoku-generator.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/lib/sudoku-generator.vala b/lib/sudoku-generator.vala
index da35d5f..5909ac5 100644
--- a/lib/sudoku-generator.vala
+++ b/lib/sudoku-generator.vala
@@ -74,7 +74,7 @@ public class SudokuGenerator : Object
 
     public async static SudokuBoard[] generate_boards_async (int nboards, DifficultyCategory category) 
throws ThreadError
     {
-        var boards_list = new ArrayList<SudokuBoard> ();
+        var boards_list = new ConcurrentList<SudokuBoard> ();
         var boards = new SudokuBoard[nboards];
         var threads = new ArrayList<Thread<void*>> ();