rustdoc: fix the search-bar layout

Now with broader compatibility.

src/librustdoc/html/layout.rs

@@ -58,11 +58,13 @@ pub fn render<T: fmt::Default, S: fmt::Default>(
 
     <nav class=\"sub\">
         <form class=\"search-form js-only\">
-            <input class=\"search-input\" name=\"search\"
-                   autocomplete=\"off\"
-                   placeholder=\"Search documentation...\"
-                   type=\"search\" />
             <button class=\"do-search\">Search</button>
+            <div class=\"search-container\">
+                <input class=\"search-input\" name=\"search\"
+                       autocomplete=\"off\"
+                       placeholder=\"Search documentation...\"
+                       type=\"search\" />
+            </div>
         </form>
     </nav>