fix goimports error in test.pb.go file. (#248)

- modified generate.sh to run goimports on generated file.
- added additional line before generated comment to fix golint error in test.pb.go

Author: rghetia

internal/testpb/generate.sh

@@ -2,6 +2,8 @@
 # generate .pb.go file from .proto file.
 set -e
 protoc --go_out=plugins=grpc:. test.proto
-echo '//go:generate ./generate.sh
+echo '
+//go:generate ./generate.sh
 ' >> test.pb.go
+goimports -w test.pb.go