Update git.autistici.org/ai3/go-common digest to 39e01d3

...or/github.com/openzipkin/zipkin-go/reporter/serializer.go

vendor/github.com/openzipkin/zipkin-go/sample.go

vendor/github.com/openzipkin/zipkin-go/span.go

...or/github.com/openzipkin/zipkin-go/span_implementation.go

vendor/github.com/openzipkin/zipkin-go/span_options.go

vendor/github.com/openzipkin/zipkin-go/tags.go

vendor/github.com/openzipkin/zipkin-go/tracer.go

vendor/github.com/openzipkin/zipkin-go/tracer_options.go

vendor/go.opencensus.io/.gitignore

vendor/go.opencensus.io/.travis.yml

vendor/go.opencensus.io/AUTHORS

vendor/go.opencensus.io/CONTRIBUTING.md

vendor/go.opencensus.io/Makefile

vendor/go.opencensus.io/README.md

vendor/go.opencensus.io/appveyor.yml

vendor/go.opencensus.io/go.mod

vendor/go.opencensus.io/go.sum

vendor/go.opencensus.io/internal/tagencoding/tagencoding.go

vendor/go.opencensus.io/metric/metricdata/label.go

vendor/go.opencensus.io/metric/metricdata/metric.go