Update JSON C++ lib to fix MSVC compilation
Update JSON C++ lib to fix MSVC compilation

Visual Studio 16.5 broke JSON for Modern C++'s implicit cast to
std::string.

Update bundled copy to current snapshot to fix.

See https://github.com/nlohmann/json/issues/2006

alexhenrie/poedit,PKRoma/poedit,nawawi/poedit,alexhenrie/poedit,nawawi/poedit,vslavik/poedit,nawawi/poedit,vslavik/poedit,nawawi/poedit,alexhenrie/poedit,PKRoma/poedit,vslavik/poedit,alexhenrie/poedit,alexhenrie/poedit,PKRoma/poedit,vslavik/poedit,PKRoma/poedit,vslavik/poedit,PKRoma/poedit,nawawi/poedit