Can not downgrade bundler for heroku - ruby-on-rails

Question

I am trying to push my project to heroku and I am getting this error.
Your Ruby version is 2.3.0, but your Gemfile specified 2.3.0
remote: Bundler Output: Warning: the running version of Bundler is older than the version that created the lockfile. We suggest you upgrade to the latest version of Bundler by running `gem install bundler`.
I am also using rvm.
It seems like the heroku bundler uses 1.11.2 so I am trying to downgrade my version from 1.12.5.
I did gem uninstall bundler then gem install bundler --version '1.11.2'
However when I do bundler -v, it's still showing 1.12.5
But when I do gem uninstall bundler, it shows
Successfully uninstalled bundler-1.11.2
I still can't push and I am getting that error. Please help.

Answer 1

Please follow these steps;
http://rubygems.rubyforge.org/rubygems-update/UPGRADING_rdoc.html
And one more thing I think your bundler is installed in the rvm default gemset i.e. system gemset.
Try checking this;
Do rvm list in terminal, this will give you output like this;
rvm rubies
ruby-2.0.0-p643 [ x86_64 ]
=* ruby-2.1.4 [ x86_64 ]
ruby-2.2.1 [ x86_64 ]
ruby-2.2.4 [ x86_64 ]
Now do rvm gemset list; this will give you out put as this;
(default)
global
some-gemset
Check which gemset its used in your system, it can be identified as => global whenever you do the rvm gemset list.
Now when you identified in which gemset you currently in, do something like this rvm use 1.9.2#global
Then;
gem uninstall bundler
Or in a single step you can do it like this;
rvm #global do gem uninstall bundler
And then install your desired bundler version like this;
gem install bundler --version '1.11.2'
Hope this might help you.