added python3-dev to build dependencies for dockerfile on debian9

docker/Dockerfile.debian9

@@ -51,6 +51,7 @@ RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install --assume-ye
   pkg-config \
   python \
   python-dev \
+  python3-dev \
   unixodbc-dev \
   uuid-dev \
   xsltproc \