Would be useful to turn off in test env as well as production

[hoegrammer]

When running unit tests the errors are caught which means you don't get an informative stack trace. Might it be useful to treat NODE_ENV=test the same as production, or perhaps to allow the user to set options as to which envs to catch errors in?

[gaearon]

We now explicitly suggest using env in .babelrc: gaearon/babel-plugin-react-transform#13. Feel free to send a PR to change this README too.