Fix incorrect variable reference in "apply the history step"

Closes whatwg#10703.

Author: domenic

source

@@ -102790,6 +102790,9 @@ location.href = '#foo';</code></pre>
       <p>In both cases, let <var>afterPotentialUnloads</var> be the following steps:</p>
 
       <ol>
+       <li><p>Let <var>previousEntry</var> be <var>navigable</var>'s <span
+       data-x="nav-active-history-entry">active session history entry</span>.</p></li>
+
        <li><p>If <var>changingNavigableContinuation</var>'s <span
        data-x="changing-nav-continuation-update-only">update-only</span> is false, then
        <span>activate history entry</span> <var>targetEntry</var> for
@@ -102801,7 +102804,7 @@ location.href = '#foo';</code></pre>
        <var>changingNavigableContinuation</var>'s <span
        data-x="changing-nav-continuation-update-only">update-only</span>,
        <var>scriptHistoryLength</var>, <var>scriptHistoryIndex</var>, <var>navigationType</var>,
-       <var>entriesForNavigationAPI</var>, and <var>displayedEntry</var>.</p></li>
+       <var>entriesForNavigationAPI</var>, and <var>previousEntry</var>.</p></li>
 
        <li><p>If <var>targetEntry</var>'s <span data-x="she-document">document</span> is equal to
        <var>displayedDocument</var>, then perform <var>updateDocument</var>.</p></li>