message: fix macro ONNX_DISALLOW_COPY_AND_ASSIGN bug
diff: #define ONNX_DISALLOW_COPY_AND_ASSIGN(TypeName) \
  TypeName(const TypeName&) = delete; \
  - void operator=(const TypeName&) = delete
  + TypeName& operator=(const TypeName&) = delete
  namespace ONNX_NAMESPACE {
  