Update git submodules

* Update docs/submodules/parser from branch 'master'
  - Merge "update verigraph"
  - update verigraph

    JIRA: PARSER-154

    code optimizations about graph manipulation and formula generation.

    Change-Id: Idebef19b128281aa2bc40d1aeab6e208c7ddd93d
    Signed-off-by: serena.spinoso <serena.spinoso@polito.it>

diff --git a/docs/submodules/parser b/docs/submodules/parser
index 96de938..8153ff1 160000 (submodule)
--- a/docs/submodules/parser
+++ b/docs/submodules/parser
@@ -1 +1 @@
-Subproject commit 96de9387460091e7cf0dc5fde1afaa637a8b2b79
+Subproject commit 8153ff1bac0ec3664c777302396698e4fb5f34b9