Editorial: fix typo in decoding="" attribute description

Author: grgr-dkrk

source

@@ -27751,7 +27751,7 @@ was an English &lt;a href="/wiki/Music_hall">music hall&lt;/a> singer, ...</code
 
   <p>In order to aid the user agent in deciding whether to perform synchronous or asynchronous
   decode, the <code data-x="attr-img-decoding">decoding</code> attribute can be set on
-  <code>img</code> elements. The possible values of of the <code
+  <code>img</code> elements. The possible values of the <code
   data-x="attr-img-decoding">decoding</code> attribute are the following <dfn>image decoding
   hint</dfn> keywords:</p>