Update git submodules

* Update docs/submodules/sdc.git from branch 'master'
  to 8b53d639026267aef71659fe292a75e47555265f
  - Manifest is optional in ETSI SOL004 manifest

    SOL004MetaDirectoryValidtor enforces all files contained in an ETSI SOL004 CSAR are included in the manifest file, however the manifest itself is not mandatory to include in the manifest

    Signed-off-by: MichaelMorris <michael.morris@est.tech>
    Issue-ID: SDC-3057
    Change-Id: I460071ecbd21578edb0603f600da0ac1ea877539

diff --git a/docs/submodules/sdc.git b/docs/submodules/sdc.git
index c74aa44..8b53d63 160000 (submodule)
--- a/docs/submodules/sdc.git
+++ b/docs/submodules/sdc.git
@@ -1 +1 @@
-Subproject commit c74aa44beabc303a5cf709625ee802dcd1bb9f5d
+Subproject commit 8b53d639026267aef71659fe292a75e47555265f