Update CHANGELOG

Author: mbostock

CHANGELOG.md

@@ -4,7 +4,7 @@
 
 Released September 24, 2021.
 
-Rect, bar, and rule marks now accept an *interval* option that allows you to derive *x1* and *x2* from *x*, or *y1* and *y2* from *y*, where appropriate. For example, using d3.utcDay as the interval creates rects that span from UTC midnight to UTC midnight, bounding the associated time instant. The interval is typically specifed as a [D3 time interval](https://github.com/d3/d3-time/blob/main/README.md), but may be any object with two methods: *interval*.floor(*x*) returns the start of the interval *x1* for the given *x*, while *interval*.offset(*x*) returns the end of the interval *x2* for the given interval start *x*. If the interval is specified as a number *n*, *x1* and *x2* are the two consecutive multiples of *n* that bracket *x*.
+Rect, bar, and rule marks now accept an *interval* option that allows you to derive *x1* and *x2* from *x*, or *y1* and *y2* from *y*, where appropriate. For example, using d3.utcDay as the interval creates rects that span from UTC midnight to UTC midnight, bounding the associated time instant. The interval is typically specifed as a [D3 time interval](https://github.com/d3/d3-time/blob/main/README.md), but may be any compatible object which implements *interval*.floor and *interval*.offset: *interval*.floor(*x*) returns the start of the interval *x1* for the given *x*, while *interval*.offset(*x*) returns the end of the interval *x2* for the given interval start *x*. If the interval is specified as a number *n*, *x1* and *x2* are the two consecutive multiples of *n* that bracket *x*.
 
 The new Plot.normalize and Plot.window methods return map methods for use in conjunction with Plot.map. This allows greater flexibility; for example, you can apply separate window methods to *y1* and *y2* to produce Bollinger bands.