Add missing log-trace feature to Cargo.toml

This fixes a new compiler warning for unexpected cfgs.

Author: robin-nitrokey

Cargo.toml

@@ -43,6 +43,7 @@ c-stubs = []
 log-all = []
 log-none = []
 log-info = []
+log-trace = []
 log-debug = []
 log-warn = []
 log-error = []