Upgrade dependencies

vendor/git.autistici.org/ai3/go-common/clientutil/dns.go

vendor/git.autistici.org/ai3/go-common/clientutil/watcher.go

vendor/git.autistici.org/ai3/go-common/serverutil/http.go

vendor/git.autistici.org/ai3/go-common/serverutil/tls.go

vendor/github.com/beorn7/perks/quantile/stream.go

vendor/github.com/cenkalti/backoff/context.go

vendor/github.com/cenkalti/backoff/exponential.go

vendor/github.com/cenkalti/backoff/retry.go

vendor/github.com/coreos/go-systemd/NOTICE

vendor/github.com/coreos/go-systemd/daemon/sdnotify.go

vendor/github.com/coreos/go-systemd/daemon/watchdog.go

vendor/github.com/golang/protobuf/LICENSE

vendor/github.com/golang/protobuf/proto/Makefile

vendor/github.com/golang/protobuf/proto/clone.go

vendor/github.com/golang/protobuf/proto/decode.go

vendor/github.com/golang/protobuf/proto/deprecated.go

vendor/github.com/golang/protobuf/proto/discard.go

vendor/github.com/golang/protobuf/proto/encode.go

vendor/github.com/golang/protobuf/proto/equal.go

vendor/github.com/golang/protobuf/proto/extensions.go