Updated import paths, README and CONTRIBUTING.

CONTRIBUTING.md

@@ -13,6 +13,5 @@ process of contribution:
 # Developers tools
 - [Protocol buffers compiler (protoc)](https://github.com/protocolbuffers/protobuf) - Google's data interchange format.
 - [protoc-gen-gogofaster](https://github.com/gogo/protobuf/tree/master/protoc-gen-gogofaster) - protoc plugin implements Go bindings for protocol buffers.
-- [goimports](golang.org/x/tools/cmd/goimports) - Command goimports updates your Go import lines, adding missing ones and removing unreferenced ones.
-- [dep](https://github.com/golang/dep#installation) - Go dependency management tool. Yeah, we still use vendor.
+- [goimports](https://golang.org/x/tools/cmd/goimports) - Command goimports updates your Go import lines, adding missing ones and removing unreferenced ones.
 - [Ginkgo](https://github.com/onsi/ginkgo#set-me-up) - BDD Testing Framework for Go.

Makefile

@@ -6,7 +6,7 @@ LDFLAGS= -ldflags '-X github.com/bold-commerce/protoc-gen-struct-transformer/gen
 
 re-generate-example:
 	protoc \
-		--proto_path=vendor/github.com/gogo:. \
+		--proto_path=$(GOPATH)/pkg/mod/github.com/gogo:. \
 		--struct-transformer_out=package=transform,debug=false,helper-package=helpers:. \
 		--gogofaster_out=Moptions/annotations.proto=github.com/bold-commerce/protoc-gen-struct-transformer/options:. \
 		./example/message.proto

README.md

@@ -17,6 +17,9 @@
   * [Run protoc](#run-protoc)
   * [Use generated functions in your gRPC server implementation.](#use-generated-functions-in-your-grpc-server-implementation)
   * [CLI parameters](#cli-parameters)
+* [Troubleshooting](#troubleshooting)
+  * [make generate returns an error](#make-generate-returns-an-error)
+    * ["protobuf@v1.3.1/gogoproto/gogo.proto" was not found or had errors.](#protobufv131gogoprotogogoproto-was-not-found-or-had-errors)
 
 <!-- vim-markdown-toc -->
 
@@ -154,6 +157,7 @@ which should be placed into $PATH to be available for `protoc`.
 If you're going to make changes to plugin, use `go get ...` or `git clone ...`
 
 ```shell
+% export GO111MODULE=on
 % go get -u -d github.com/bold-commerce/protoc-gen-struct-transformer
 % cd $GOPATH/src/github.com/bold-commerce/protoc-gen-struct-transformer
 // make changes
@@ -259,3 +263,15 @@ Usage of protoc-gen-struct-transformer:
   -version
         Print current version.
 ```
+## Troubleshooting
+
+### make generate returns an error
+#### "protobuf@v1.3.1/gogoproto/gogo.proto" was not found or had errors.
+`gogo.proto` file which is used for gogo-specific options is imported from
+go modules cache. In order to fill out the cache run:
+
+```shell
+% export GO111MODULE=on
+% go build
+```
+and run `make generate` again.

example/message.proto

@@ -7,7 +7,7 @@ option (transformer.go_models_file_path) = "example/model/model.go";
 option go_package = "example"; // Package name for pb.go
 
 import "options/annotations.proto";
-import "protobuf/gogoproto/gogo.proto"; // for gogoproto options
+import "protobuf@v1.3.1/gogoproto/gogo.proto"; // for gogoproto options
 import "google/protobuf/timestamp.proto";
 
 message TheOne{