Generate ActiveRecord 5.0 style migrations

Test that ActiveRecord::Migration responds to .[] before using
.current_version, as .current_version is used in previous versions
but for different purposes.

padrino-gen/lib/padrino-gen/generators/components/orms/activerecord.rb

@@ -152,7 +152,19 @@ def create_model_file(name, options={})
  create_file(model_path, model_contents,:skip => true)
end

if defined?(ActiveRecord::Migration) && ActiveRecord::Migration.respond_to?(:[])
AR_MIGRATION = (<<-MIGRATION) unless defined?(AR_MIGRATION)
class !FILECLASS! < ActiveRecord::Migration[#{ActiveRecord::Migration.current_version}]
  def self.up
    !UP!
  end

  def self.down
    !DOWN!
  end
end
MIGRATION
else
AR_MIGRATION = (<<-MIGRATION) unless defined?(AR_MIGRATION)
class !FILECLASS! < ActiveRecord::Migration
  def self.up
@@ -164,6 +176,7 @@ def self.down
  end
end
MIGRATION
end

AR_MODEL_UP_MG = (<<-MIGRATION).gsub(/^/,'    ') unless defined?(AR_MODEL_UP_MG)
create_table :!TABLE! do |t|