Update git submodules

* Update docs/submodules/nfvbench from branch 'stable/euphrates'
  - Documentation update

    Change-Id: I5b96349d2eb2fc21a15dde6adbd72f7e84c737bf
    Signed-off-by: ahothan <ahothan@cisco.com>

diff --git a/docs/submodules/nfvbench b/docs/submodules/nfvbench
index 8683295..d6d7766 160000 (submodule)
--- a/docs/submodules/nfvbench
+++ b/docs/submodules/nfvbench
@@ -1 +1 @@
-Subproject commit 86832955f65bf9efdce512c35ff2e1074f45d370
+Subproject commit d6d77669fcb13c779d869929a95ec9e9474b3fcf