Fix header on search page

Author: josevalim

assets/js/handlebars/templates/search-results.handlebars

@@ -2,7 +2,7 @@
   {{#if value}}
     Search results for <em>{{value}}</em>
   {{else}}
-    Invalid Search
+    Invalid search
   {{/if}}
 
   <button class="settings display-settings">

lib/ex_doc/formatter/html/templates/search_template.eex

@@ -4,7 +4,7 @@
 <div id="search">
   <h1>
     <%= settings_button_template() %>
-    <span>Page not found</span>
+    <span></span>
   </h1>
 
   <div class="loading"><div></div><div></div><div></div><div></div></div>