Add bootstrap cfg
diff --git a/Cargo.toml b/Cargo.toml
index 535f6c9..6fa1717 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -172,6 +172,7 @@
 elided_lifetimes_in_paths = "warn"
 explicit_outlives_requirements = "warn"
 unsafe_op_in_unsafe_fn = "warn"
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(bootstrap)'] }
 unused_extern_crates = "warn"
 unused_lifetimes = "warn"
 unreachable_pub = "warn"