Merge branch 'index_snippet' into 'master'

Add index for snippet's updated_at

@DouweM We are ordering by `updated_at` but there is no index.

cc @yorickpeterse 

See merge request !2768

db/migrate/20160209130428_add_index_to_snippet.rb

+class AddIndexToSnippet < ActiveRecord::Migration
+  def change
+    add_index :snippets, :updated_at
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20160129135155) do
+ActiveRecord::Schema.define(version: 20160209130428) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -771,6 +771,7 @@ ActiveRecord::Schema.define(version: 20160129135155) do
   add_index "snippets", ["created_at"], name: "index_snippets_on_created_at", using: :btree
   add_index "snippets", ["expires_at"], name: "index_snippets_on_expires_at", using: :btree
   add_index "snippets", ["project_id"], name: "index_snippets_on_project_id", using: :btree
+  add_index "snippets", ["updated_at"], name: "index_snippets_on_updated_at", using: :btree
   add_index "snippets", ["visibility_level"], name: "index_snippets_on_visibility_level", using: :btree
 
   create_table "spam_logs", force: :cascade do |t|