It’s not something to worry about unless you need to use the project with Bundler v1 anywhere. The only non-compatibility will be for developers or environments who can only have Bundler v1 installed.
From the documentation:
What happens if my application needs Bundler 2, but I only have
Bundler 1 installed?
If you try to use Bundler 1 on an application
that requires Bundler 2, you’ll see an error message explaining that
you need to install Bundler 2. Go ahead and run gem install bundler,
and then it should work.
This is an irreversible change, so you can’t go backwards.
Can I downgrade my application from Bundler 2 to Bundler 1?
Bundler 2 does not provide a way to downgrade a Gemfile back to Bundler 1.
Instead, we recommend checking in your Gemfile and Gemfile.lock before
you upgrade your application. That way, if something goes wrong, you
can revert to the previous commit and go back to using Bundler 1.
If it updated automatically and you didn’t specify the --bundle switch, that might be because one of the gems you updated had a dependency on Bundler itself at a more recent version. Check your Gemfile.lock and see if any gems have Bundler as a dependency.
