Update example to not user profile.id

Bitbucket does not pass back an `id` property on its profile, rather, it's probably best to use the `username` property.

Here is an example of what I get back for the `profile` value in the strategy callback:

    { 
      provider: 'bitbucket',
      username: 'jacob4u2',
      displayName: 'Jacob Gable',
      name: { familyName: 'Gable', givenName: 'Jacob' },
      _raw: '<some long json string>',
      _json: {
        repositories: [<Repos>],
        user: {
          username: 'jacob4u2',
          first_name: 'Jacob',
          last_name: 'Gable',
          is_team: false,
          avatar: 'https://secure.gravatar.com/avatar/2ed341e37f2c3ef44296019c9e9829bf?d=https%3A%2F%2Fdwz7u9t8u8usb.cloudfront.net%2Fm%2F309704b5e60d%2Fimg%2Fdefault_avatar%2F32%2Fuser_blue.png&s=32',
          resource_uri: '/1.0/users/jacob4u2'
        }
    }