`rowSum()` breaks for `Int` + `Float`

```kt
dataFrameOf("a", "b")(1, 2f)[0].rowSum()
```
results in `java.lang.IllegalStateException: Can not find common number type for class kotlin.Int and class kotlin.Float`

should be considered in https://github.com/Kotlin/dataframe/issues/961