doc: Update link in release notes.

Change-Id: If00485b88611f9ce7ab37491000bf7f9e0c8df57
Signed-off-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/5753
Reviewed-by: Anand Avati <avati@redhat.com>
Tested-by: Anand Avati <avati@redhat.com>