Update spec reference in duk_instanceof() API doc

website/api/duk_instanceof.yaml

@@ -8,7 +8,7 @@ stack: |
 
 summary: |
   <p>Compare values at <code>idx1</code> and <code>idx2</code> using the
-  Ecmascript <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.8.6">instanceof</a>
+  Ecmascript <a href="https://www.ecma-international.org/ecma-262/6.0/#sec-instanceofoperator">instanceof</a>
   operator.  Returns 1 if <code>val1 instanceof val2</code>, 0 if not.  Throws an error
   if either index is invalid; <code>instanceof</code> itself also throws errors for
   invalid argument types.</p>