Thread safety of calls that result in transitions

Possible problem case: eg. reading the current state name while transitioning. There is no locking going on as far as I can see. Am I missing something?

Eg.:

``` go
fsm := NewFSM(....)
go func() {
    fmt.Println(fsm.Current())
}()
go func() {
    fsm.Event("...")
}()
```
