errata: typo in Ex 12.7

errata.html

@@ -224,6 +224,13 @@ pre {
     (Thanks to Shinji Dosaka, 2016-07-15.)
   </p>
 
+  <p>
+    <b>p.341, Exercise 12.7</b>: For "encoder" and
+    "<code>json.Encoder</code>", read "decoder" and
+    "<code>json.Decoder</code>", respectively.
+    (Thanks to Yoshiki Shibata, 2016-08-27.)
+  </p>
+
   <p>
     <b>p.347, Exercise 12.8</b>: For "like <code>json.Marshal</code>",
     read "like <code>json.Unmarshal</code>".