[compilation issue] new version of nanogui requires C++17, but ext/CMakeLists.txt still uses C++14

[LukasRuppert]

Hi, with the updated version of nanogui, you're also using a few C++17 features, e.g. here.
You may want to adjust the ext/CMakeLists.txt to use C++17 or even C++20 when available.

g++ 11.2.1 will otherwise not compile Nori.
clang++ 11 seems to work fine, though.