Support for non integer ID

before 
```
user = User.first.global_id
#<ActiveModel::GlobalID:0x007fc03365fe50 @gid="GlobalID-User-7ef9b614-353c-43a1-a203-ab2307851990">
user.model_id     #=> "7ef9b614"
```

after 
```
user =User.first.global_id
#<ActiveModel::GlobalID:0x007fc03365fe50 @gid="GlobalID-User-7ef9b614-353c-43a1-a203-ab2307851990">
user.model_id     #=> "7ef9b614-353c-43a1-a203-ab2307851990"
```