build: disable `-Wnon-virtual-dtor` compiler warning

See also named-data/NFD@0a05f7aea6e56a32139a6271de1f98536153a86a

Change-Id: Id615459e8b9db20ae54851b3b4808b4c5e94d3b0
diff --git a/src/handles/read-handle.hpp b/src/handles/read-handle.hpp
index 780a9c6..4e53f97 100644
--- a/src/handles/read-handle.hpp
+++ b/src/handles/read-handle.hpp
@@ -31,10 +31,10 @@
 
 class ReadHandle : public noncopyable
 {
-
 public:
   using DataPrefixRegistrationCallback = std::function<void(const ndn::Name&)>;
   using DataPrefixUnregistrationCallback = std::function<void(const ndn::Name&)>;
+
   struct RegisteredDataPrefix
   {
     ndn::RegisteredPrefixHandle hdl;