Fix extra space when there are unused limits
Fix extra space when there are unused limits

When plotting only a subset of the a discrete variable,
the computation of the plot limits was using all the
limits. This left empty spaces on the plot.

   df = diamonds.query('carat > 1')
   d = (ggplot(df, aes('cut', 'clarity'))
        + geom_point()
        + scale_x_discrete(limits=['Fair','Ideal']))
   d

has2k1/plotnine,has2k1/plotnine