Add jest config

React folks often use Jest. I think it would be good to add it’s config by default.

I get lots of errors like:

  3:1  'describe' is not defined.  no-undef
  4:3  'test' is not defined.      no-undef

I guess better defaults would be to allow them in test files

[sheerun]

Hmm suddenly it’s working for me as well, I think it’s because I’ve experimented with .lyntrc and made something like this and forgot about it:

{
  "env": {
    "jest": true
  }
}

It seems such .lyntrc is incorrect overrides CLI flag (usually CLI flags have priority over configuration).

[sheerun]

I guarantee that 90% of react devs are using Jest for testing. Also I think the discussion about these variables going non-global in Jest is not relevant, as status quo for this moment is that they are global and Lynt is supposed to be “Zero configuration by default” 😃