Update libp2p requirement from 0.17.0 to 0.18.1

[dependabot-preview[bot]]

Updates the requirements on libp2p to permit the latest version.

Changelog

Sourced from libp2p's changelog.

Version 0.18.1 (2020-04-17)

• libp2p-swarm: Make sure inject_dial_failure is called in all situations. PR 1549

Version 0.18.0 (2020-04-09)

• libp2p-core: Treat connection limit errors as pending connection errors. PR 1546

• libp2p-core-derive: Disambiguate calls to NetworkBehaviour::inject_event. PR 1543

• libp2p-floodsub: Allow sent messages seen as subscribed. PR 1520

• libp2p-kad: Return peers independent of record existence. PR 1544

• libp2p-wasm-ext: Fix "parsed is null" errors being thrown. PR 1535

Version 0.17.0 (2020-04-02)

• libp2p-core: Finished "identity hashing" for peer IDs migration. PR 1460

• libp2p-core: Remove poll_broadcast. PR 1527

• libp2p-core, libp2p-swarm: Report addresses of closed listeners. PR 1485

• libp2p-core: Support for multiple connections per peer and configurable connection limits. See [PR #1440](libp2p/rust-libp2p#1440), [PR #1519](libp2p/rust-libp2p#1519) and [issue #912](libp2p/rust-libp2p#912) for details.

• libp2p-swarm: Pass the cause of closing a listener to inject_listener_closed. PR 1517

• libp2p-swarm: Support for multiple connections per peer and configurable connection limits. See [PR #1440](libp2p/rust-libp2p#1440), [PR #1519](libp2p/rust-libp2p#1519) and [issue #912](libp2p/rust-libp2p#912) for details.

• libp2p-swarm: The SwarmEvent now returns more events. PR 1515

• libp2p-swarm: New protocols_handler::multi module. PR 1497

• libp2p-swarm: Allow configuration of outbound substreams. PR 1521

• libp2p-kad: Providers returned from a lookup are now deduplicated. PR 1528

... (truncated)

Commits

• 87b5efb Make sure inject_dial_failure is called (#1549)
• 77a34c0 protocols/kad/query/peers/closest: Make at_capacity use max (#1548)
• aa71158 Publish 0.18.0 (#1547)
• d2eebf2 Treat connection limit errors as pending connection errors. (#1546)
• 803eb10 Disambiguate calls to NetworkBehaviour::inject_event (#1543)
• 8adf474 Fix parsed is null error (#1535)
• 80ea2f6 feat: allow sent messages seen as subscribed (#1520)
• c1191d5 protocols/kad/behaviour: Return peers independent of record existence (#1544)
• 8411087 Bump async-tls (#1532)
• 3eec3cc Update CHANGELOG.md with 0.17.0 (#1541)
• See full diff in compare view

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[dependabot-preview[bot]]

Looks like libp2p is no longer updatable, so this is no longer needed.