sort co_author name

app/controllers/desktop/co_authors_controller.rb

@@ -1,7 +1,7 @@
 class Desktop::CoAuthorsController < ApplicationController
   def index
-    @co_authors = CoAuthor.where(name_id: current_user.id).order(["co_author desc"])
-    nils, not_nils = @co_authors.partition {|p| p.email.nil? }
+    nils, not_nils = CoAuthor.where(name_id: current_user.id)\
+                     .asc(:co_author).partition{|p| p.email.nil?}
     @co_authors = not_nils + nils
     @co_author_relations = CoAuthorRelation.all