update swarm v1.2.8-rc1

Signed-off-by: Nishant Totla <[email protected]>

library/swarm

@@ -5,5 +5,8 @@ Maintainers: Alexandre Beslic <[email protected]> (@abronan),
              Victor Vieux <[email protected]> (@vieux)
 GitRepo: https://github.com/docker/swarm-library-image.git
 
+Tags: 1.2.8-rc1
+GitCommit: b28650fbd0f447b821505d2ec18667fbbde8a108
+
 Tags: 1.2.7, latest
 GitCommit: b741365fdf375bb7409314b4a161a91290935d3f