No parallel processing if on windows.

Author: drvinceknight

axelrod/tournament.py

@@ -110,7 +110,7 @@ def play(self, build_results=True, filename=None,
         if not build_results and not filename:
             warnings.warn("Tournament results will not be accessible since build_results=False and no filename was supplied.")
 
-        if processes is None:
+        if (processes is None) or (on_windows):
             self._run_serial(progress_bar=progress_bar)
         else:
             self._run_parallel(processes=processes, progress_bar=progress_bar)