Bump mirror submodule to 2018.3.1 version

Change-Id: I1bceec2008348f6289dd657cfcb6f83c2536208b
diff --git a/classes/cluster/mcp-offline/infra/mirror b/classes/cluster/mcp-offline/infra/mirror
index ec90b72..d2d8163 160000
--- a/classes/cluster/mcp-offline/infra/mirror
+++ b/classes/cluster/mcp-offline/infra/mirror
@@ -1 +1 @@
-Subproject commit ec90b72e0c0bae70d4e81c96b088a0778266a716
+Subproject commit d2d81634204832c8a68bb5e8105ceee63a121f2c