Fix compile warning when compiling with clang
Fix compile warning when compiling with clang

clang version 10.0.0

    src/gui-qt/project.h:61:24: warning: class with destructor marked 'final' cannot be inherited from [-Wfinal-dtor-non-final-class]
        virtual ~Project() final;
                           ^

undisbeliever/untech-editor,undisbeliever/untech-editor