Center X-axis label 

chart-05.png
@@ -22,6 +22,7 @@
     title              => 'Product Sales',
     y_label            => 'Units Shipped (Millions)',
     x_label            => 'Product Sales by Year',
+    x_label_position   => 0.5,
     transparent        => 0,
     bgclr              => 'white',
     dclrs              => ['#ff782a', '#6daa3a', '#4d7296'],