network: Update litep2p to v0.5.0 (#4570)

This is a small patch release that makes the `FindNode` command a bit
more robst:

- The `FindNode` command now retains the K (replication factor) best
results.
- The `FindNode` command has been updated to handle errors and
unexpected states without panicking.

- kad: Refactor FindNode query, keep K best results and add tests
([#114](paritytech/litep2p#114))

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Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>