D3.JS BusData Graph - Stage 5
The Y-Axis has 10 ticks and have added grid lines for the
y-axis which occurr every 5 ticks. This is to make it easier to
judge the height of the bar without it overwhelming the user.
I have also delayed the animation on the PassengersOut so that
each set of data is shown one at a time.
I have also changed the bar colours to gradients
and added the values to each bar.