Implement Envie.values()

[KATT]

Use case:

const envie = require('envie')
const Joi = require('joi')

const { PORT } = envie({
  PORT: Joi
    .number()
    .min(0)
    .default(0)
    .description('Port on which the HTTP server will listen'),
}).values()

server.listen(PORT)

[coveralls]

Coverage increased (+0.01%) to 99.296% when pulling aa6bfac on KATT:feature/values() into b638df2 on Floby:master.

[Floby]

Oh hey, sorry I'm not very quick on noticing pull requests !
I like this one, thank you. I think it qualifies nicely as the next minor release. I'll let you know here when it's released. Gotta accept the #9 first an publish it as a patch.