Fix misuse of 'phase' wrt to wave functions in Chapter 16

Closes marijnh#547

Author: marijnh

16_game.md

@@ -417,7 +417,7 @@ the sine function useful for modeling a wavy motion.
 {{index pi}}
 
 To avoid a situation where all coins move up and down synchronously,
-the starting phase of each coin is randomized. The _((phase))_ of
+the starting phase of each coin is randomized. The period of
 `Math.sin`'s wave, the width of a wave it produces, is 2π. We multiply
 the value returned by `Math.random` by that number to give the coin a
 random starting position on the wave.

html/errata.html

@@ -93,6 +93,10 @@ <h2>Chapter 15</h2>
 
 <h2>Chapter 16</h2>
 
+<p><strong>Page 271</strong> <em>Actors</em>: Near the bottom of the
+page, the book incorrectly uses the term <em>phase</em> (of a sinus
+wave) where it should say <em>period</em>.</p>
+
 <p><strong>Page 278</strong> <em>Motion and Collision</em>: The code
 that defines the <code>touches</code> method unintentionally (though
 harmlessly) used <code>var</code> instead of <code>let</code> to