Merge pull request #135 from mateusz/fix-head

Fix docs not coming up for HEAD requests.

code/controllers/DocumentationViewer.php

@@ -177,7 +177,7 @@ class DocumentationViewer extends Controller implements PermissionProvider
     public function handleAction($request, $action)
     {
         // if we submitted a form, let that pass
-        if (!$request->isGET()) {
+        if (!$request->isGET() && !$request->isHEAD()) {
             return parent::handleAction($request, $action);
         }