koa: esInterop compatibility

[ishitatsuyuki]

TODO:

• Update CHANGELOG.md with your change (include reference to issue & this PR)
• (not applicable) Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

Close #1393

[apollo-cla]

@ishitatsuyuki: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[ishitatsuyuki]

Can someone assign a reviewer?

[hwillson]

Thanks for this @ishitatsuyuki. We're changing the esModuleInterop approach for the entire repo, so when #1699 is merged in, the changes in this PR will no longer be necessary. We should have it merged shortly. Thanks for your work on this!