Update cube.h

wrong: vec2<T>	maxNrmDvPos(numeric_limits<T>::min(),numeric_limits<T>::min());
numeric_limits<T>::min() is zero.
that is why ,projectedsize() function did not work fine,
so I fixe it up like this,		
vec2<T>	maxNrmDvPos(-numeric_limits<T>::max(),-numeric_limits<T>::max());