build: update cligen submodule

This is to respect SOURCE_DATE_EPOCH and to stop using the "error"
function from <error.h>.

Signed-off-by: Daiki Ueno <ueno@gnu.org>

diff --git a/cligen b/cligen
index ed2ed7b19a5bcbc0f39505722058befc923eeeda..59911854af60377b045ec8db88ae969b5bad1f66 160000 (submodule)
--- a/cligen
+++ b/cligen
@@ -1 +1 @@
-Subproject commit ed2ed7b19a5bcbc0f39505722058befc923eeeda
+Subproject commit 59911854af60377b045ec8db88ae969b5bad1f66