Make history.go() default to 0

Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=28790

source

@@ -79450,7 +79450,7 @@ x === this; // true</pre>
   <pre class="idl">interface <dfn>History</dfn> {
   readonly attribute long <span data-x="dom-history-length">length</span>;
   readonly attribute any <span data-x="dom-history-state">state</span>;
-  void <span data-x="dom-history-go">go</span>(optional long delta);
+  void <span data-x="dom-history-go">go</span>(optional long delta = 0);
   void <span data-x="dom-history-back">back</span>();
   void <span data-x="dom-history-forward">forward</span>();
   void <span data-x="dom-history-pushState">pushState</span>(any data, DOMString title, optional DOMString? url = null);
@@ -79575,10 +79575,10 @@ x === this; // true</pre>
   Initially, its value must be null.</p>
 
   <p>When the <dfn><code data-x="dom-history-go">go(<var>delta</var>)</code></dfn> method is
-  invoked, if the argument to the method was omitted or has the value zero, the user agent must act
-  as if the <code data-x="dom-location-reload">location.reload()</code> method was called instead.
-  Otherwise, the user agent must <span>traverse the history by a delta</span> whose value is the
-  value of the method's argument.</p>
+  invoked, if <var>delta</var> is zero, the user agent must act as if the
+  <code data-x="dom-location-reload">location.reload()</code> method was called instead. Otherwise,
+  the user agent must <span>traverse the history by a delta</span> whose value is
+  <var>delta</var>.</p>
 
   <p>When the <dfn><code data-x="dom-history-back">back()</code></dfn> method is invoked, the user
   agent must <span>traverse the history by a delta</span> &#x2212;1.</p>