Axes not fixed if 3-D smooths are present

[StefanoMezzini]

draw does not allow scales = 'fixed' if ti() terms are plotted. It would be nice to be able to have a common axis for 2-D smooths (i.e. s()) and the z axis of ti() terms (i.e. the color scale).

plot_grid(draw(m, scales = 'fixed'),
          draw(m, scales = 'fixed', select = 1:3))

[gavinsimpson]

Thanks @StefanoMezzini I have fixed the bug (the 1-d smooths should have been fixed but not the 2-d one). I have also adapted the code so that all plots will have a fixed scale now if requested.

[gavinsimpson]

These changes will be in version 0.4.1 which I am packaging up for CRAN at the moment. So hopefully there in the next few days.