build: use recent protobuf in docker

Dockerfile

@@ -5,5 +5,10 @@ FROM debian:9
 # install build tools and dependencies
 
 RUN apt-get update && apt-get install -y \
-    build-essential git python python-ecdsa gcc-arm-none-eabi \
-    protobuf-compiler libprotobuf-dev python-protobuf
+    build-essential git python python-ecdsa gcc-arm-none-eabi curl
+RUN apt-get install -y unzip python-pip
+
+ENV PROTOBUF_VERSION=3.4.0
+RUN curl -LO "https://github.com/google/protobuf/releases/download/v${PROTOBUF_VERSION}/protoc-${PROTOBUF_VERSION}-linux-x86_64.zip"
+RUN unzip "protoc-${PROTOBUF_VERSION}-linux-x86_64.zip" -d /usr
+RUN pip2 install "protobuf==${PROTOBUF_VERSION}"