Actualizado plugin Redmine Questions 1.0.0 light

plugins/redmine_questions/db/migrate/002_add_viewing_migration.rb

@@ -1,10 +1,29 @@
-class AddViewingMigration < ActiveRecord::Migration
+# This file is a part of Redmine Q&A (redmine_questions) plugin,
+# Q&A plugin for Redmine
+#
+# Copyright (C) 2011-2018 RedmineUP
+# http://www.redmineup.com/
+#
+# redmine_questions is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# redmine_questions is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with redmine_questions.  If not, see <http://www.gnu.org/licenses/>.
 
+class AddViewingMigration < Rails.version < '5.1' ? ActiveRecord::Migration : ActiveRecord::Migration[4.2]
   def self.up
-    ActiveRecord::Base.create_viewings_table
+    unless table_exists?(:viewings)
+      ActiveRecord::Base.create_viewings_table
+    end
   end
 
   def self.down
-    ActiveRecord::Base.drop_viewings_table
   end
 end