[grilo] typo: remove double comma in doc

[Victor Toso <victortoso src gnome org>]

commit 96a2e4af3f5bffc3c2d97b75824802392eb74c0f
Author: Victor Toso <victortoso gnome org>
Date:   Tue Mar 30 22:00:32 2021 +0200

    typo: remove double comma in doc

 src/data/grl-data.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/data/grl-data.c b/src/data/grl-data.c
index 455121dd..988cd809 100644
--- a/src/data/grl-data.c
+++ b/src/data/grl-data.c
@@ -1029,7 +1029,7 @@ grl_data_add_int64 (GrlData *data,
  * As example, let's think in three related keys, K1, K2 and K3, and then thinks
  * we have added several values for those keys, as:
  *
- *   (V10, V20, V30),, (V11, NULL, V31), (V12, NULL, V32)
+ *   (V10, V20, V30), (V11, NULL, V31), (V12, NULL, V32)
  *
  * Therefore, when invoking grl_data_length (data, K2) it will return 3:
  * considering K2 and the related keys (K1 and K3), there are 3 values.