[gnome-builder] buildstage: fix cast

[Christian Hergert <chergert src gnome org>]

commit 9878b67e500b39389434c63fc31ab618bda8a215
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Sat May 26 10:10:24 2018 +0200

    buildstage: fix cast

 src/libide/buildsystem/ide-build-stage.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/libide/buildsystem/ide-build-stage.c b/src/libide/buildsystem/ide-build-stage.c
index 467bc625b..41b179f1c 100644
--- a/src/libide/buildsystem/ide-build-stage.c
+++ b/src/libide/buildsystem/ide-build-stage.c
@@ -541,7 +541,7 @@ ide_build_stage_execute_async (IdeBuildStage       *self,
 
       g_clear_object (&priv->stdout_stream);
 
-      priv->stdout_stream = g_steal_pointer (&stream);
+      priv->stdout_stream = G_OUTPUT_STREAM (g_steal_pointer (&stream));
     }
 
   IDE_BUILD_STAGE_GET_CLASS (self)->execute_async (self, pipeline, cancellable, callback, user_data);