Hide new file link if not branch HEAD

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

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

@@ -10,11 +10,12 @@
         = link_to truncate(title, length: 40), project_tree_path(@project, path)
       - else
         = link_to title, '#'
-  \/
-  %li
-    = link_to project_new_tree_path(@project, @id), title: 'New file', id: 'new-file-link' do
-      %small
-        %i.icon-plus.light
+  - if @repository.branch_names.include?(@ref)
+    \/
+    %li
+      = link_to project_new_tree_path(@project, @id), title: 'New file', id: 'new-file-link' do
+        %small
+          %i.icon-plus.light
 
 %div#tree-content-holder.tree-content-holder
   %table#tree-slider{class: "table_#{@hex_path} tree-table" }