Use system bold for filename

diff --git a/ast b/ast
index f1ea3ebd6f37d05a0cbcf18d042cc3c55841d4b3..bc17eb88eaca2457ac207aa24ad2ed0552cc8170 160000 (submodule)
--- a/ast
+++ b/ast
@@ -1 +1 @@
-Subproject commit f1ea3ebd6f37d05a0cbcf18d042cc3c55841d4b3
+Subproject commit bc17eb88eaca2457ac207aa24ad2ed0552cc8170