[libgames-support] scores: add_score cancellable parameter should not have a default value

[Michael Catanzaro <mcatanzaro src gnome org>]

commit ed942da2e1a71ea8a504e886230f83328ca0e6d9
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Sun Feb 14 12:52:54 2016 -0600

    scores: add_score cancellable parameter should not have a default value
    
    There should be a warning for this; the GAsyncReadyCallback needs to be
    passed after the cancellable, so everyone has to pass null here anyway.

 games/scores/context.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/games/scores/context.vala b/games/scores/context.vala
index e86ea43..dfc677d 100644
--- a/games/scores/context.vala
+++ b/games/scores/context.vala
@@ -192,7 +192,7 @@ public class Context : Object
     }
 
     /* Return true if a dialog was launched on attaining high score */
-    public async bool add_score (long score_value, Category category, Cancellable? cancellable = null) 
throws Error
+    public async bool add_score (long score_value, Category category, Cancellable? cancellable) throws Error
     {
         var high_score_added = false;
        /* We need to check for game_window to be not null because thats a way to identify if add_score is 
being called by the test file.