Update git submodules

* Update docs/submodules/doctor from branch 'stable/euphrates'
  - Merge "Euphrates release note" into stable/euphrates
  - Euphrates release note

    Change-Id: I961640e662a2d11ce183859978e0c9737ac5f386
    Signed-off-by: Ryota MIBU <r-mibu@cq.jp.nec.com>
    (cherry picked from commit 46beef591b7e60da522ced5de8930ec025d8c326)

diff --git a/docs/submodules/doctor b/docs/submodules/doctor
index bca7b0f..55ad897 160000 (submodule)
--- a/docs/submodules/doctor
+++ b/docs/submodules/doctor
@@ -1 +1 @@
-Subproject commit bca7b0f906b3c325b76308f139aca72f190f9f37
+Subproject commit 55ad897310d1258679911acce80fd4bb878d9fef