gnulib: update to the latest

update to a version with parse_gnu_standard_options_only()

diff --git a/gnulib b/gnulib
index 341723e1b879d70a08afdf4d8c566606f267e081..e3970fb9891668bd9dbc94daca18dc0d42b7e466 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 341723e1b879d70a08afdf4d8c566606f267e081
+Subproject commit e3970fb9891668bd9dbc94daca18dc0d42b7e466