Merge branch 'quote_string' into 'master'

db/migrate/20150425164647_remove_duplicate_tags.rb

 class RemoveDuplicateTags < ActiveRecord::Migration
   def up
     select_all("SELECT name, COUNT(id) as cnt FROM tags GROUP BY name HAVING COUNT(id) > 1").each do |tag|
-      duplicate_ids = select_all("SELECT id FROM tags WHERE name = '#{tag["name"]}'").map{|tag| tag["id"]}
+      tag_name = quote_string(tag["name"])
+      duplicate_ids = select_all("SELECT id FROM tags WHERE name = '#{tag_name}'").map{|tag| tag["id"]}
       origin_tag_id = duplicate_ids.first
       duplicate_ids.delete origin_tag_id