update to twig 1.6.4

diff --git a/twig b/twig
index 9154d27..ff61094 160000 (submodule)
--- a/twig
+++ b/twig
@@ -1 +1 @@
-Subproject commit 9154d27622a349fb1986cb9d48014c464a0e9d5b
+Subproject commit ff61094aa374808c3f2c1a385352226090e37ecf