The ruby docker image I use for development currently comes with bundler 1.17.2 installed as its default version. Attempting to update the minor version of the gem via traditional methods has lead to either version 2 being installed, or the 1.17.3 binary not being found.

If you’re looking to upgrade from 1.17.2 to 1.17.3 the following should do it:

gem install bundler -v 1.17.2
gem uninstall bundler -v 1.17.2
# You will want to find this on your machine - try the `gem env` command
# to check possible places. You just want to delete the gemspec for 1.17.2
rm /usr/local/lib/ruby/gems/2.6.0/specifications/default/bundler-1.17.2.gemspec
gem install bundler -v 1.17.3