Fix typo in Chapter 8

Author: marijnh

08_error.txt

@@ -75,7 +75,7 @@ and encounters the nonsensical action.
 produce a `NaN` (not a number) or undefined value. And the program
 happily continues, convinced that it's doing something meaningful. The
 mistake will manifest itself only later, after the bogus value has
-traveled though several functions. It might not trigger an error at
+traveled through several functions. It might not trigger an error at
 all but silently cause the program's output to be wrong. Finding the
 source of such problems can be difficult.
 

html/errata.html

@@ -36,6 +36,12 @@ <h2>Chapter 2</h2>
 variable <code>name</code> whose values are implicitly converted to
 strings.</p>
 
+<h2>Chapter 8</h2>
+
+<p><strong>Page 140</strong> (Programmer Mistakes): In the third
+paragraph, the text reads “though several functions”, which should be
+“th<strong>r</strong>ough several functions”.
+
 <h2>Chapter 9</h2>
 
 <p><strong>Page 157</strong> (Repeating Parts of a Pattern): The