Fix numerical key bindings on different keyboard layouts

This fix should ensure that the spell book will always work for players playing with different keyboard layouts. That is because instead of relying on key.keyCode or key.which which could contain different values it checks for key.code which in the case of the numerical keys always equals to value Digit1-0.

There might be a better way to fix this issue, but I did not want to manipulate the code more than is necessary.