multiaddr_to_socketaddr test failing on master

[tomaka]

https://github.com/paritytech/rust-libp2p/blob/710dec31108385e43e871aab50c385d1abdd0e24/libp2p-tcp-transport/src/lib.rs#L155-L161

This test has been there for a long time and it has suddenly started failing, probably after a cargo update.

[tomaka]

Turns out this was caused by rust-lang/rust#46270.
Updating my Rust compiler also fixed the issue.