Issue title: Building proto with docker fails
 Issue body: Seems like building is not working via Docker `make docker-generate`. I'm not familar enough with protoc to know what it means by the plugin failure.

I ran this on two machines to ensure it can be replicated: AWS Instance and my MBP.

```
[snip]
go: finding github.com/mholt/caddy v0.0.0-20180907212407-13a54dbdda25
 -> building cli 42605bd-dev
 -> building cni-ipam 42605bd-dev
 -> Built dev version 42605bd (linux/amd64)
Removing intermediate container d25e59d175b5
 ---> 55835e7cb1df
Successfully built 55835e7cb1df
Successfully tagged stellar-dev:latest
protoc-gen-grpc-gateway: program not found or is not executable
--grpc-gateway_out: protoc-gen-grpc-gateway: Plugin failed with status code 1.
2018/11/06 17:29:13 protoc -I.:/go/src/github.com/ehazlett/stellar/vendor/github.com/gogo/protobuf:/go/src/github.com/ehazlett/stellar/vendor/github.com/gogo/googleapis:/go/src/github.com/ehazlett/stellar/vendor:/go/src:/usr/local/include:/usr/include --grpc-gateway_out=import_path=github.com/ehazlett/stellar/api/services/application/v1,Mgogoproto/gogo.proto=github.com/gogo/protobuf/gogoproto,Mgoogle/api/annotations.proto=github.com/gogo/googleapis,Mgoogle/api/http.proto=github.com/gogo/googleapis,Mgoogle/protobuf/any.proto=github.com/gogo/protobuf/types,Mgoogle/protobuf/descriptor.proto=github.com/gogo/protobuf/protoc-gen-gogo/descriptor,Mgoogle/protobuf/duration.proto=github.com/gogo/protobuf/types,Mgoogle/protobuf/empty.proto=github.com/gogo/protobuf/types,Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types:/go/src /go/src/github.com/ehazlett/stellar/api/services/application/v1/application.proto
make: *** [Makefile:38: generate] Error 123
tar: Unrecognized archive format
tar: Error exit delayed from previous errors.
make: *** [docker-generate] Error 1
```
 Comments: 
 Comment 0: There was a missing proto binary.  This should be fixed.  Thanks!
{'source': 'GithubIssues', 'repo_name_with_owner': 'ehazlett/stellar', 'issue_id': 377959407, 'repo_stars': 1098.0}