Use 'react-native-get-random-values' instead of 'react-native-crypto' and 'react-native-randombytes'

[alxroyer]

react-native-crypto and react-native-randombytes are stated as deprecated.

Both point to the react-native-get-random-values alternative.

[alxroyer]

Let me know if it's worth I submit a pull-request on that point. I'd be glad to contribute.