Add mistake in chapter 16 to errata

Issue marijnh#472

Author: marijnh

html/errata.html

@@ -36,6 +36,12 @@ <h2>Chapter 10</h2>
 needs it own private scope“, it should say “<em>its</em> own private
 scope“.
 
+<h2>Chapter 16</h2>
+
+<p><strong>Page 285</strong> <em>Pausing the Game</em>: The text
+refers to the <code>arrow</code> binding, where it should
+say <code>arrowKeys</code>.</p>
+
 <h2>Chapter 20</h2>
 
 <p><strong>Page 369</strong> (1st) <em>Directory