Update README.

Author: mbostock

README.md

@@ -2,7 +2,7 @@
 
 Utilities for array manipulation: ordering, summarizing, searching, etc.
 
-When using D3—and with data visualization in general—you tend to do a lot of **array manipulation**. That’s because D3’s canonical representation of data is an array. Some common forms of array manipulation include taking a contiguous slice (subset) of an array, filtering an array using a predicate function, and mapping an array to a parallel set of values using a transform function. Before looking at the set of utilities that D3 provides for arrays, you should familiarize yourself with the powerful [array methods built-in to JavaScript](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype).
+When using D3—and with data visualization in general—you tend to do a lot of array manipulation. That’s because D3’s canonical representation of data is an array. Some common forms of array manipulation include taking a contiguous slice (subset) of an array, filtering an array using a predicate function, and mapping an array to a parallel set of values using a transform function. Before looking at the set of utilities that D3 provides for arrays, you should familiarize yourself with the powerful [array methods built-in to JavaScript](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype).
 
 JavaScript includes **mutator methods** that modify the array: