I looked at your Gem. In order to get it working, rename lib/xdan_datetimepicker_rails.rb to lib/xdan-datetimepicker-rails.rb.
In your Rails project, uninstall your old gem and install the new one. To make sure it's installed properly:
$ rails c
> pp MyRailsApp::Application.assets.paths
You should see an array of paths that are in the asset pipeline. Look for:
/gem/path/to/xdan-datetimepicker-rails-0.0.1/app/assets/javascripts
/gem/path/to/xdan-datetimepicker-rails-0.0.1/app/assets/stylesheets
NOTE: Restart rails c
and/or rails s
if you're not seeing it.
Finally, in order to use the assets:
app/assets/javascript/application.js
//= require jquery.xdan.datetimepicker
app/assets/stylesheets/stylesheet.css.scss
*= require jquery.xdan.datetimepicker