Drop engines field in package.json

[ranyitz]

Thanks for this awesome project!

We are trying to use it inside of Jest, But Jest only supports node 6 and above. That's why I've opened #64

There is another option, suggested here jestjs/jest#6442 (comment). We'll use prompts without transpilation because it should run only on developers machines, which probably already have node > 8.

The only problem is that Jest still supports node version 6, and will fail if we'll use prompts as a dependency due to the engines property in package.json.

@terkelg Can we drop the engines restriction and add a manual message instead?

[terkelg]

Can you confirm everything is working?

[ranyitz]

Seems to be working perfectly, prompts now supports node > 6.

@terkelg Thanks 😄