Fix docker compilation
One of the latest commits introduced C++17 code. Thus, we cannot use the default CentOS GCC4 anymore in Docker when building the AppImage.
This MR changes to GCC7
Edited by Axel Loewe
One of the latest commits introduced C++17 code. Thus, we cannot use the default CentOS GCC4 anymore in Docker when building the AppImage.
This MR changes to GCC7