`ctrl-[` exits insert mode

[axelfahy]

Closes #85.

This PR allows using ctrl-[ to exit insert mode, which was not working on Firefox.

Please finish the following when submitting a pull request:

• [x] Add a line to History.md briefly documenting the change.

If this is a release, additionally do the following:

• [x] Bump the package version in package.json
• [x] Update the dependencies in package.json
• [x] Run jlpm install to update yarn.lock

Thanks!