Use upstream https://github.com/oKcerG/SortFilterProxyModel repo for git submodule
The 3rdparty/SortFilterProxyModel submodule currently points to https://github.com/atraczyk/SortFilterProxyModel, which is a fork of https://github.com/atraczyk/SortFilterProxyModel, which is itself a fork of https://github.com/atraczyk/SortFilterProxyModel.
Since the forks do not include original work and are 40 commits behind the original project, I think it'd be clearer to point the 3rdparty/SortFilterProxyModel git submodule to it.