Add const to BinMapper::CopyTo

include/LightGBM/bin.h

@@ -143,7 +143,7 @@ public:
   * \brief Seirilizing this object to buffer
   * \param buffer The destination
   */
-  void CopyTo(char* buffer);
+  void CopyTo(char* buffer) const;
 
   /*!
   * \brief Deserilizing this object from buffer

src/io/bin.cpp

@@ -302,7 +302,7 @@ int BinMapper::SizeForSpecificBin(int bin) {
   return size;
 }
 
-void BinMapper::CopyTo(char * buffer) {
+void BinMapper::CopyTo(char * buffer) const {
   std::memcpy(buffer, &num_bin_, sizeof(num_bin_));
   buffer += sizeof(num_bin_);
   std::memcpy(buffer, &is_trival_, sizeof(is_trival_));