generated files: update google/protobuf v1.3.5, protoc v3.14.0 and fix install for go modules

hack/dockerfiles/generated-files.Dockerfile

@@ -2,21 +2,21 @@
 
 # protoc is dynamically linked to glibc to can't use golang:1.10-alpine
 FROM golang:1.13-buster AS gobuild-base
-ARG PROTOC_VERSION=3.1.0
-ARG GOGO_VERSION=master
+# https://github.com/golang/protobuf/blob/v1.3.5/.travis.yml#L15
+ARG PROTOC_VERSION=3.11.4
+ARG GOGO_VERSION=v1.3.2
 RUN apt-get update && apt-get --no-install-recommends install -y \
-	git \
 	unzip \
 	&& true
 RUN wget -q https://github.com/google/protobuf/releases/download/v${PROTOC_VERSION}/protoc-${PROTOC_VERSION}-linux-x86_64.zip && unzip protoc-${PROTOC_VERSION}-linux-x86_64.zip -d /usr/local
 
-RUN go get -d github.com/gogo/protobuf/protoc-gen-gogofaster \
+RUN git clone https://github.com/gogo/protobuf.git /go/src/github.com/gogo/protobuf \
 	&& cd /go/src/github.com/gogo/protobuf \
 	&& git checkout -q $GOGO_VERSION \
 	&& go install ./protoc-gen-gogo ./protoc-gen-gogofaster ./protoc-gen-gogoslick
 
-ARG PROTOBUF_VERSION=v1.3.3
-RUN go get -d github.com/golang/protobuf/protoc-gen-go \
+ARG PROTOBUF_VERSION=v1.3.5
+RUN git clone https://github.com/golang/protobuf.git /go/src/github.com/golang/protobuf \
 	&& cd /go/src/github.com/golang/protobuf \
 	&& git checkout -q $PROTOBUF_VERSION \
 	&& go install ./protoc-gen-go

hack/update-generated-files

@@ -4,11 +4,13 @@
 set -eu
 
 gogo_version=$(awk '$1 == "github.com/gogo/protobuf" { print $2 }' go.mod)
+protobuf_version=$(awk '$3 == "github.com/golang/protobuf" { print $4 }' go.mod)
 output=$(mktemp -d -t buildctl-output.XXXXXXXXXX)
 
 buildxCmd build \
   --target "update" \
   --build-arg "GOGO_VERSION=$gogo_version" \
+  --build-arg "PROTOBUF_VERSION=$protobuf_version" \
   --output "type=local,dest=$output" \
   --file "./hack/dockerfiles/generated-files.Dockerfile" \
   .