Mark one errata as fixed in the 4th reprint

Author: marijnh

html/errata.html

@@ -60,7 +60,7 @@ <h2>Chapter 10</h2>
 
 <h2>Chapter 11</h2>
 
-<p><strong>Page 189/190</strong> <em>Networks are Hard</em>: The text
+<p><strong>Page 189/190</strong> (4th) <em>Networks are Hard</em>: The text
 under the code that defines <code>request</code> claims the function
 will give up after four attempts and a second. In fact, it gives up
 after three attempts, in three-quarter second.</p>