Change mcp version to 2018.3.1.

Change-Id: I7a4fbaf2f8af09183192746ecd0bb8561d6dafe8
diff --git a/init.yml b/init.yml
index 0e1de1d..223848d 100644
--- a/init.yml
+++ b/init.yml
@@ -39,7 +39,7 @@
 - service.docker.host
 parameters:
   _param:
-    apt_mk_version: '2018.3.0'
+    apt_mk_version: '2018.3.1'
     aptly_gpg_keypair_id: A8272E04
     aptly_gpg_passphrase: ""
     aptly_server_secure: true