Compilation warning: 'tuple_size' defined as a class template here but previously declared as a struct template

[ibc]

• What is the issue you have?

../include/json.hpp:1799:1: warning: 'tuple_size' defined as a class template here but previously declared as a struct template [-Wmismatched-tags]
class tuple_size<::nlohmann::detail::iteration_proxy_value<IteratorType>>
^
/usr/lib/gcc/x86_64-linux-gnu/5.4.0/../../../../include/c++/5.4.0/tuple:798:5: note: did you mean class here?
    struct tuple_size;

• Which compiler and operating system are you using?

Linux Debian
clang version 7.0.0

• Did you use a released version of the library or the version from the develop branch?

3.5.0

[nickaein]

This issue is already discussed here: #1401