Hide new file link if not branch HEAD

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/projects/tree/_tree.html.haml

@@ -10,6 +10,7 @@
         = link_to truncate(title, length: 40), project_tree_path(@project, path)
       - else
         = link_to title, '#'
+  - if @repository.branch_names.include?(@ref)
     \/
     %li
       = link_to project_new_tree_path(@project, @id), title: 'New file', id: 'new-file-link' do