Use release version of protobuf.

[jgiles]

Referencing the release version is preferred, and plays nicer when
resolving transitive deps.

This change was created by manually altering the constraint and then
running "dep ensure" with version 0.4.1 of dep. There were some
Gopkg.lock formatting changes, but this change DOES NOT use version
0.5.0 of dep, which introduces breaking Gopkg.lock changes.

[jgiles]

make all is breaking on my machine both on master and on this branch:

$ make all
go vet github.com/grpc-ecosystem/go-grpc-middleware github.com/grpc-ecosystem/go-grpc-middleware/auth github.com/grpc-ecosystem/go-grpc-middleware/logging github.com/grpc-ecosystem/go-grpc-middleware/logging/logrus github.com/grpc-ecosystem/go-grpc-middleware/logging/logrus/ctxlogrus github.com/grpc-ecosystem/go-grpc-middleware/logging/zap github.com/grpc-ecosystem/go-grpc-middleware/logging/zap/ctxzap github.com/grpc-ecosystem/go-grpc-middleware/recovery github.com/grpc-ecosystem/go-grpc-middleware/retry github.com/grpc-ecosystem/go-grpc-middleware/tags github.com/grpc-ecosystem/go-grpc-middleware/tags/logrus github.com/grpc-ecosystem/go-grpc-middleware/tags/zap github.com/grpc-ecosystem/go-grpc-middleware/testing github.com/grpc-ecosystem/go-grpc-middleware/testing/gogotestproto github.com/grpc-ecosystem/go-grpc-middleware/testing/testproto github.com/grpc-ecosystem/go-grpc-middleware/tracing/opentracing github.com/grpc-ecosystem/go-grpc-middleware/util/backoffutils github.com/grpc-ecosystem/go-grpc-middleware/util/metautils github.com/grpc-ecosystem/go-grpc-middleware/validator
# github.com/grpc-ecosystem/go-grpc-middleware/tracing/opentracing_test
tracing/opentracing/interceptors_test.go:248: github.com/grpc-ecosystem/go-grpc-middleware/vendor/github.com/opentracing/opentracing-go/mocktracer.MockSpanContext composite literal uses unkeyed fields
make: *** [vet] Error 2

[codecov-io]

Codecov Report

Merging #163 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #163   +/-   ##
=======================================
  Coverage   72.88%   72.88%           
=======================================
  Files          36       36           
  Lines        1313     1313           
=======================================
  Hits          957      957           
  Misses        308      308           
  Partials       48       48

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 15ea740...3f8cc69. Read the comment docs.