Resolve modernize-use-equals-default

https://github.com/dtolnay/cxx/issues/500
diff --git a/include/cxx.h b/include/cxx.h
index 8d7e96f..f87d333 100644
--- a/include/cxx.h
+++ b/include/cxx.h
@@ -477,7 +477,7 @@
 }
 
 template <typename T>
-Box<T>::Box() noexcept {}
+Box<T>::Box() noexcept = default;
 #endif // CXXBRIDGE1_RUST_BOX
 
 #ifndef CXXBRIDGE1_RUST_VEC