can't use same email on multiple teams :(

#### Problem

This would prevent a user from using the same email for multiple teams
#### Examples

https://github.com/astroscrum/rails-api/blob/master/app/models/player.rb#L32

```
validates_uniqueness_of :email
```

https://github.com/astroscrum/rails-api/blob/master/app/models/player.rb#L36

```
player = find_by_email(email)
```
