Update git submodules

* Update docs/submodules/doctor from branch 'master'
  - Merge "Update the maintenance design document"
  - Update the maintenance design document

    JIRA: DOCTOR-125

    Change-Id: Ideb1482fa026213bfe5ebc7a1da89cfed634950f
    Signed-off-by: Tomi Juvonen <tomi.juvonen@nokia.com>

diff --git a/docs/submodules/doctor b/docs/submodules/doctor
index 4639f15..f9e1e3b 160000 (submodule)
--- a/docs/submodules/doctor
+++ b/docs/submodules/doctor
@@ -1 +1 @@
-Subproject commit 4639f15e6db2f1480b41f6fbfd11d70312d4e421
+Subproject commit f9e1e3b1ae4be80bc2dc61d9c4213c81c091ea72