Update to the newest gnulib.

diff --git a/gnulib b/gnulib
index 3766806904396257b098d800c04c996306ff9517..3691a095c1eb6579d32551b2af02550bc3f6cccc 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit 3766806904396257b098d800c04c996306ff9517
+Subproject commit 3691a095c1eb6579d32551b2af02550bc3f6cccc