Install less extra junk

Author: Peter Amstutz

Dockerfile

@@ -9,10 +9,10 @@ RUN apt-get update && \
     sh -c 'echo deb https://oss-binaries.phusionpassenger.com/apt/passenger stretch main > /etc/apt/sources.list.d/passenger.list'
 
 RUN apt-get update && \
-    apt-get install -y passenger python-setuptools build-essential python-dev python-pip git && \
+    apt-get install -y --no-install-recommends passenger python-setuptools build-essential python-dev python-pip git && \
     pip install pip==9.0.3
 
-RUN apt-get install -y libcurl4-openssl-dev libssl1.0-dev
+RUN apt-get install -y --no-install-recommends libcurl4-openssl-dev libssl1.0-dev
 
 ARG version