I have a forked Github repo which is used by my app deployed on heroku. I included it in my Gemfile like this :
gem 'service-client', :git => 'https://github.com/blabla/client-stuff'
Now I changed some parts of the forked repo, which requires no changes in my heroku app.
So how can I make my heroku app, rebundle or do the bundle install or whatever to pick up the latest changes from https://github.com/blabla/client-stuff master branch?
You should update gem localy and write changes to Gemfile.lock by bundle update service-client then commit changes and push to origin. Heroku update you gemset when look in to the changes in Gemfile.lock.
Unfortunately it does require changes in your heroku app. It requires the newest gem version. You will have to push up to heroku again so that it can re bundle your Gemfile.
there is not way to run a bundle update on heroku itself because this could cause git fast-forward issues along with other unexpected consequences where a newer gem does not work appropriately.
Heroku is a production environment and all changes should be tested locally before deploying
