Configure environment variables

[yamsellem]

NODE_ENV is set to test by this plugin, but it's not possible to add our own environnement variables. This could be helpful on some ALLOW_CONFIG_MUTATIONS=true cases with the config npm module (for example).

Thanks for the great work anyway ^^.

[sindresorhus]

Doesn't seem like something this plugin should solve. On the command-line you can specify environment variables. Nothing specific to AVA. In Atom, you could use a plugin to do so: https://atom.io/packages/atomenv

Can you confirm that's working ok? If so, I'll document it.