Socks Proxy requires Socks Version

If someone tries to set the socks proxy they
also need to declare the socks version.

Closes #1008

webdriver-spec.html

@@ -2053,8 +2053,14 @@ <h3>Proxy</h3>
 
  <li><p>If <var>proxy</var> does not have an <a>own property</a> for
   "<code>proxyType</code>" return an <a>error</a> with <a>error
-  code</a> <a>invalid argument</a>. Otherwise return <a>success</a>
-  with data <var>proxy</var>.
+  code</a> <a>invalid argument</a>.
+
+ <li><p>If <var>proxy</var> has an <a>own property</a> for
+  "<code>socksProxy</code>" and does not have an <a>own property</a>
+  for "<code>socksVersion</code>" return an <a>error</a> with <a>error
+  code</a> <a>invalid argument</a>.
+
+ <li><p>Return <a>success</a> with data <var>proxy</var>.
 </ol>
 
 <p>A <dfn>proxy configuration object</dfn> is a