support for rails 4.0

Author: Fivell

.travis.yml

@@ -1,4 +1,9 @@
 script: bundle exec rspec spec
+env:
+  matrix:
+    - RAILS=4.0.13
+    - RAILS=4.1.5
+    - RAILS=4.2.6
 rvm:
   - 2.1.5
   - 2.2.0

Gemfile

@@ -4,7 +4,7 @@ source 'https://rubygems.org'
 gemspec
 group :test do
   gem 'sprockets-rails', '2.3.3'
-  gem 'rails',  '4.2.0'
+  gem 'rails', "#{ENV['RAILS']}" || '4.2.6'
   gem 'rspec-rails'
   gem 'activeadmin', github: 'activeadmin'  , ref: 'd787029e5523be2eb2ed99816eb0cecca2b72862'
   gem 'coveralls', require: false # Test coverage website. Go to https://coveralls.io

lib/active_admin_datetimepicker/base.rb

@@ -1,12 +1,9 @@
 module ActiveAdminDatetimepicker
   module Base
-    mattr_accessor :default_datetime_picker_options do
-      {}
-    end
-
-    mattr_accessor :format do
-      '%Y-%m-%d %H:%M'
-    end
+    mattr_accessor :default_datetime_picker_options
+    @@default_datetime_picker_options = {}
+    mattr_accessor :format
+    @@format = '%Y-%m-%d %H:%M'
 
     def html_class
       'date-time-picker'