Add quote issue in footer example to errata

Author: marijnh

html/errata.html

@@ -43,6 +43,12 @@ <h2>Chapter 11</h2>
 its parentheses distributed incorrectly. One closing parentheses from
 the second line should be moved to the end of the last line.</p>
 
+<h2>Chapter 13</h2>
+
+<p><strong>Page 238</strong> (Creating Nodes): In the example code
+that adds a footer, the double quotes should be <em>around</em> the emdash
+(—) character, not after it.</p>
+
 <h2>Chapter 14</h2>
 
 <p><strong>Page 242</strong> (Mouse Motion): The example