Update CHANGELOG

Author: mbostock

CHANGELOG.md

@@ -12,7 +12,7 @@ The new [box mark](./README.md#box) generates a horizontal or vertical boxplot s
 Plot.boxX(morley, {x: "Speed", y: "Expt"}).plot({x: {grid: true, inset: 6}})
 ```
 
-[Plot’s shorthand syntax](https://observablehq.com/@observablehq/plot-shorthand) has been expanded. The [bar mark](./README.md#bar) now supports one-dimensional shorthand: if no *options* are specified, then Plot.barX and Plot.barY can be used to visualize an array of numbers. This shorthand also now applies to the [rect mark](./README.md#rect) and the [vector mark](./README.md#vector). The [area mark](./README.md#area) now supports two-dimensional shorthand: if no *options* are specified, then Plot.area can be used to visualize an array of [x, y] tuples (similar to Plot.line).
+[Plot’s shorthand syntax](https://observablehq.com/@observablehq/plot-shorthand) has been expanded. The [bar mark](./README.md#bar) now supports one-dimensional shorthand: if no *options* are specified, then Plot.barX and Plot.barY can be used to visualize an array of numbers. This shorthand also now applies to the [rect mark](./README.md#rect) and the [vector mark](./README.md#vector). The [area mark](./README.md#area) now supports two-dimensional shorthand: if no *options* are specified, then Plot.area can be used to visualize an array of *xy*-tuples, similar to Plot.line.
 
 <img src="./img/bar-shorthand.png" width="640" alt="a bar chart of twenty random values">