fix: golang/protobuf version
fix: golang/protobuf version

`github.com/golang/protobuf`:
- `github.com/prometheus/client_golang` (no version)
- `github.com/gogo/protobuf` (no version)
- `google.golang.org/appengine` (no version)
- `github.com/matttproud/golang_protobuf_extensions` (no version)

State:
- Current version: 2bba0603135d7d7f5cb73b2125beeda19c09f4ef
- Glide suggest: 8616e8ee5e20a1704615e6c8d7afcdac06087a67

Force to keep the current version.

Refs
- https://github.com/golang/protobuf/commit/2bba0603135d7d7f5cb73b2125beeda19c09f4ef (Mar 31, 2017) next commit the Apr 27, 2017.
- https://github.com/golang/protobuf/commit/8616e8ee5e20a1704615e6c8d7afcdac06087a67 (8 Jun 2016)

vdemeester/traefik,adityacs/traefik,thomasbach76/traefik,vdemeester/traefik,mmatur/traefik,mmatur/traefik,mvdstam/traefik,aantono/traefik,nmengin/traefik,tanyadegurechaff/traefik,SantoDE/traefik,bparli/traefik,timoreimann/traefik,tanyadegurechaff/traefik,nmengin/traefik,marco-jantke/traefik,mvdstam/traefik,thomasbach76/traefik,bparli/traefik,bparli/traefik,timoreimann/traefik,tanyadegurechaff/traefik,adityacs/traefik,ldez/traefik,mmatur/traefik,containous/traefik,mildis/traefik,mildis/traefik,dtomcej/traefik,aantono/traefik,aantono/traefik,FriggaHel/traefik,marco-jantke/traefik,SantoDE/traefik,mvdstam/traefik,thomasbach76/traefik,ldez/traefik,aantono/traefik,nmengin/traefik,vdemeester/traefik,timoreimann/traefik,mihaitodor/traefik,dtomcej/traefik,adityacs/traefik,EmileVauge/traefik,vdemeester/traefik,FriggaHel/traefik,martinbaillie/traefik,EmileVauge/traefik,martinbaillie/traefik,FriggaHel/traefik,marco-jantke/traefik,containous/traefik,EmileVauge/traefik,thomasbach76/traefik,mildis/traefik,mildis/traefik,SantoDE/traefik,mihaitodor/traefik,mvdstam/traefik,dtomcej/traefik,marco-jantke/traefik,ldez/traefik,containous/traefik,nmengin/traefik,martinbaillie/traefik,adityacs/traefik,dtomcej/traefik,mmatur/traefik,EmileVauge/traefik,FriggaHel/traefik,mihaitodor/traefik,bparli/traefik,timoreimann/traefik,martinbaillie/traefik,ldez/traefik,containous/traefik,aantono/traefik,tanyadegurechaff/traefik,SantoDE/traefik,mihaitodor/traefik