fix typo

Author: pchampin

index.html

@@ -3113,7 +3113,7 @@ <h3>Algorithm</h3>
                       and remove <var>container key</var> from <var>compacted item</var>.</li>
                     <li class="changed">Otherwise, if <var>container</var> includes <code>@index</code>
                       and <var>index key</var> is not <code>@index</code>,
-                      Set <var>map key</var> to the first value of <var>container key</var> in <var>compacted item</var>, if any.
+                      set <var>map key</var> to the first value of <var>container key</var> in <var>compacted item</var>, if any.
                       If there are remaining values in <var>compacted item</var>
                       for <var>container key</var>, set the value of
                       <var>container key</var> in <var>compacted item</var>