Specify version for proto-gen Docker image

Makefile

@@ -1,12 +1,13 @@
 CHAINNET?=betanet
 BINARY?=sifnoded
+GOPATH?=$(shell go env GOPATH)
 GOBIN?=${GOPATH}/bin
 NOW=$(shell date +'%Y-%m-%d_%T')
 COMMIT:=$(shell git log -1 --format='%H')
 VERSION:=$(shell cat version)
 IMAGE_TAG?=latest
 HTTPS_GIT := https://github.com/sifchain/sifnode.git
-DOCKER := $(shell which docker)
+DOCKER ?= docker
 DOCKER_BUF := $(DOCKER) run --rm -v $(CURDIR):/workspace --workdir /workspace bufbuild/buf
 
 ldflags = -X github.com/cosmos/cosmos-sdk/version.Name=sifchain \
@@ -84,23 +85,26 @@ rollback:
 ###                                Protobuf                                 ###
 ###############################################################################
 
+protoVer=v0.3
+protoImageName=tendermintdev/sdk-proto-gen:$(protoVer)
+
 proto-all: proto-format proto-lint proto-gen
 
 proto-gen:
 	@echo "Generating Protobuf files"
-	$(DOCKER) run --rm -v $(CURDIR):/workspace --workdir /workspace tendermintdev/sdk-proto-gen sh ./scripts/protocgen.sh
+	$(DOCKER) run --rm -v $(CURDIR):/workspace --workdir /workspace $(protoImageName) sh ./scripts/protocgen.sh
 .PHONY: proto-gen
 
 proto-format:
 	@echo "Formatting Protobuf files"
 	$(DOCKER) run --rm -v $(CURDIR):/workspace \
-	--workdir /workspace tendermintdev/docker-build-proto \
+	--workdir /workspace $(protoImageName) \
 	find ./ -not -path "./third_party/*" -name *.proto -exec clang-format -i {} \;
 .PHONY: proto-format
 
 # This generates the SDK's custom wrapper for google.protobuf.Any. It should only be run manually when needed
 proto-gen-any:
-	$(DOCKER) run --rm -v $(CURDIR):/workspace --workdir /workspace tendermintdev/sdk-proto-gen sh ./scripts/protocgen-any.sh
+	$(DOCKER) run --rm -v $(CURDIR):/workspace --workdir /workspace $(protoImageName) sh ./scripts/protocgen-any.sh
 .PHONY: proto-gen-any
 
 proto-swagger-gen: