Android app freezes after upgrading rxandroid 0.24 -> 0.25

I used `io.reactivex:rxandroid:0.24.0` and `io.reactivex:rxjava-string:0.22.0`

After ugrade  dependency to `io.reactivex:rxandroid:0.25.0`, app became freezes on

```
public static String joinedBy(List<String> src, String separator) {
       return StringObservable.join(Observable.from(src), separator).toBlocking().single();
}
```
