zipkin B3 headers Spanid/Traceid occasionally is 15 instead 16 digits long, zipkin-go-opentracing library needs update

[MaxWinterstein]

Do you want to request a feature or report a bug?

Bug

Did you try using a 1.7.x configuration for the version 2.0?

• Yes
• No

What did you do?

When using zipkin tracing there are B3 headers added. But, sometimes they are missing one digit.
This has already been fixed openzipkin-contrib/zipkin-go-opentracing#98 but this is not working for 1.7.10.

I guess, somewhere the build pipeline needs some push to pull the master branch again or something?

What did you expect to see?

A 16 digit Spanid
"request_X-B3-Spanid":"03b7e31b3c6e4b4b" <-- Note the 0

What did you see instead?

A 15 digit Spanid
"request_X-B3-Spanid":"3b7e31b3c6e4b4b"

Output of traefik version: (What version of Traefik are you using?)

1.7.10-alpine (docker image)

Version:      v1.7.10
Codename:     maroilles
Go version:   go1.11.6
Built:        2019-03-29_12:20:34PM
OS/Arch:      linux/amd64

What is your environment & configuration (arguments, toml, provider, platform, ...)?

    [tracing]
      backend = "zipkin"
      serviceName = "traefik"
      [tracing.zipkin]
        httpEndpoint = "http://XXX"
        debug = true
        sameSpan = false
        id128bit = true

[traefiker]

Closed by #4720.