Install Python 2 and Python 3 packages in Debian stretch. (#137)

Author: igorpeshansky

build/x86_64_stretch/Dockerfile

@@ -26,5 +26,6 @@ RUN apt-get -y update \
         make \
         pkg-config \
         python-dev \
+        python3-dev \
  && apt-get -y clean \
  && rm -rf /var/lib/apt/lists/*