gx: update go-multihash

[Stebalien]

Depends on:

• https://github.com/libp2p/go-libp2p-peer/pull/20
• https://github.com/libp2p/go-libp2p-secio/pull/23
• https://github.com/multiformats/go-multiaddr/pull/61
• https://github.com/multiformats/go-multiaddr-net/pull/33
• https://github.com/whyrusleeping/iptb/pull/37
• https://github.com/whyrusleeping/mafmt/pull/7
• https://github.com/libp2p/go-libp2p-peerstore/pull/18
• https://github.com/ipfs/go-ipfs-util/pull/6
• https://github.com/libp2p/go-libp2p-transport/pull/25
• https://github.com/libp2p/go-peerstream/pull/19
• https://github.com/libp2p/go-libp2p-loggables/pull/14
• https://github.com/libp2p/go-tcp-transport/pull/17
• https://github.com/libp2p/go-maddr-filter/pull/4
• https://github.com/libp2p/go-ws-transport/pull/28
• https://github.com/libp2p/go-addr-util/pull/9
• https://github.com/ipfs/go-cid/pull/39
• https://github.com/libp2p/go-testutil/pull/15
• https://github.com/libp2p/go-libp2p-interface-conn/pull/4
• https://github.com/libp2p/go-libp2p-interface-pnet/pull/6
• https://github.com/libp2p/go-libp2p-conn/pull/21
• https://github.com/libp2p/go-libp2p-net/pull/15
• https://github.com/libp2p/go-libp2p-metrics/pull/7
• https://github.com/libp2p/go-libp2p-interface-connmgr/pull/2
• https://github.com/libp2p/go-libp2p-host/pull/10
• https://github.com/libp2p/go-libp2p-swarm/pull/46
• https://github.com/libp2p/go-libp2p-nat/pull/4
• https://github.com/libp2p/go-libp2p-netutil/pull/16
• https://github.com/libp2p/go-libp2p-blankhost/pull/7

This PR with gx updates has been created using gx-workspace: https://github.com/ipfs/gx-workspace