Use rn-fetch-blob over react-native-fetch-blob

[jasonramirez]

react-native-fetch-blob is no longer being maintained. From https://github.com/wkh237/react-native-fetch-blob:

wkh237's last Github activity was in September 2017, and he has not reacted to emails either. This repository no longer is the main location of "react-native-fetch-blob". The owners of this fork have agreed to maintain this package: https://github.com/joltup/rn-fetch-blob

This PR aims to replace the unmaintained repo with a repo that is being maintained.

[befirst]

https://github.com/kfiroo/react-native-cached-image/pull/124

[shockdesign]

Is there any notice on when this can be merged? :)