Fix a compilation warning that started appearing with Clang 8.
diff --git a/include/fruit/impl/normalized_component_storage/normalized_component_storage_holder.h b/include/fruit/impl/normalized_component_storage/normalized_component_storage_holder.h
index 6b1b7e9..180f297 100644
--- a/include/fruit/impl/normalized_component_storage/normalized_component_storage_holder.h
+++ b/include/fruit/impl/normalized_component_storage/normalized_component_storage_holder.h
@@ -58,7 +58,7 @@
NormalizedComponentStorageHolder(const NormalizedComponentStorage&) = delete;
NormalizedComponentStorageHolder& operator=(NormalizedComponentStorageHolder&&) = delete;
- NormalizedComponentStorageHolder& operator=(const NormalizedComponentStorageHolder&) = default;
+ NormalizedComponentStorageHolder& operator=(const NormalizedComponentStorageHolder&) = delete;
// We don't use the default destructor because that would require the inclusion of
// normalized_component_storage.h. We define this in the cpp file instead.