Add correct terminator for write summary.

Author: drvinceknight

axelrod/result_set.py

@@ -739,7 +739,7 @@ def write_summary(self, filename):
         """
         summary_data = self.summarise()
         with open(filename, 'w') as csvfile:
-            writer = csv.writer(csvfile)
+            writer = csv.writer(csvfile, lineterminator='\n')
             writer.writerow(self.player._fields)
             for player in summary_data:
                 writer.writerow(player)