For each provider, just pass token property

[bahmutov]

Why use custom names inside each?

Instead of:

car = bumpercar.create({
    providers: {
      travis: {
        githubToken: creds.githubToken
      }
      circle: {
        circleToken: creds.circleToken
      }
      appVeyor: {
        appVeyorToken: creds.appVeyorToken
      }
    }
  })

should be

car = bumpercar.create({
    providers: {
      travis: {
        token: creds.githubToken
      }
      circle: {
        token: creds.circleToken
      }
      appVeyor: {
        token: creds.appVeyorToken
      }
    }
  })

This would be a breaking change