[css-images] Fix inconsistency between grammar and prose for color stops

Author: LeaVerou

css-images/Overview.bs

@@ -880,7 +880,7 @@ Gradient Color-Stops {#color-stop-syntax}
 	(It gets automatically filled in by the user agent; see below for details.)
 
 	Color stops are organized into a <dfn export>color stop list</dfn>,
-	which is a list of one or more <a>color stops</a>.
+	which is a list of two or more <a>color stops</a>.
 
 	<a>Color stops</a> are placed on a <a>gradient line</a>,
 	which defines the colors at every point of a gradient.