Fix key generation functions

[SebastienGllmt]

I noticed that both generate_ed25519 and generate_ed25519extended fail when called from Javascript with this error

self.crypto is undefined (permanently unavailable)

[ecioppettini]

Is this in node or in a browser? or perhaps in electron? I can't reproduce neither in firefox, chrome or node

[SebastienGllmt]

I tried looking into this and it seems to only happen to me for nodejs. The bug occurs in OsRng and I tried to update the package but it seems we're stuck on this version (because every version of rand_os is a breaking change by design and one of the dependencies curve25519-dalek doesn't support a higher version)