CRS-23 and CRS-24 missing flight times
The CRS-23 and CRS-24 missions are ended now but the `flight_time_sec` is still null.
Think it should be `2835720`s for [CRS-23](https://en.wikipedia.org/wiki/SpaceX_CRS-23) and `2977020`s for [CRS-24](https://en.wikipedia.org/wiki/SpaceX_CRS-24)