Rubygems updated to for Ruby 2.3.4

Change effective on 30 August 2017

The version of rubygems bundled with Ruby 2.3.4 was updated to on heroku-16 and cedar-14 stacks. You can see the current rubygems version associated with on the Ruby Version Support page.

To see the current version of rubygems installed for your app you can run:

$ heroku run bash

and then

$ ruby -v
ruby 2.3.4p301 (2017-03-30 revision 58214) [x86_64-linux]
$ gem -v