Bump backtrace-rs to enable Mach-O support on iOS.

diff --git a/library/backtrace b/library/backtrace
index a6dd47bd588c882e735675a1379d2b61719fa380..8b8ea53b56f519dd7780defdd4254daaec892584 160000 (submodule)
--- a/library/backtrace
+++ b/library/backtrace
@@ -1 +1 @@
-Subproject commit a6dd47bd588c882e735675a1379d2b61719fa380
+Subproject commit 8b8ea53b56f519dd7780defdd4254daaec892584