Bundler version on Ruby apps now 1.11.2
Change effective on 08 March 2016
The version of Bundler used while deploying and running Ruby applications is now 1.11.2. For more details on current versions see Heroku Ruby Support.
There is one known issue that has reported with this change. Applications that are accidentally using a gem with an invalid gemspec will need to fix the gemspec before being able to deploy. You can refer to the Bundler documentation for more information.