Bootstrap dropdown button not working when published to Heroku (Ruby on Rails)

I have already searched around StackOverflow and have been trying for a while to solve this, but none of them works.

Although I reordered the line in application.js and set precompile in production.rb to "true", it still does not work when pushed to Heroku. Locally, however, it is wokring fine.

Please take a look at my project file --> http://ift.tt/1pUH0Uj

I'm using ruby 2.2.4 and rails 4.2.6 on Ubuntu 14.04. Thanks