v2.1.0

Changes

• Add missing phone param for non-object configuration (now signature is vk.token(client_id, login, pass, phone))
• Add ESLint code style checks
• Use const all the way down instead of let
• Handle possible case when authorization is successful but access_token is missing in the response
• Extended testing and test coverage details
• Update request-promise to 2.0.0 from 1.0.2
• Update babel-core to 6.4.0 from 6.3.17