When you run bundle install, whatever is the latest version of bundler
installed locally will be used. Your Gemfile dependencies will be installed
and the Gemfile.lock will be marked at the bottom with a signature for the
version of bundler that was used.
# Gemfile.lock
...
BUNDLED WITH
1.1.17On future bundle install calls, a matching major version of Bundler will be
used. If you'd like to migrate from 1.x.x to 2.x.x or vice versa, or even if
you want to explicitly change minor versions, you can run:
$ bundle update --bundler=2.2.4This will bundle your project with 2.2.4 and update the BUNDLED WITH
section to reflect that.
Use the version that makes sense for you with the --bundler flag.