try to use alpine to reduce image size

Dockerfile

@@ -1,9 +1,6 @@
-FROM python:3.5
+FROM python:3.5-alpine
 
-RUN apt-get update && apt-get install -y \
-    supervisor \
-    netcat \
-    && rm -rf /var/lib/apt/lists/*
+RUN apk add --no-cache supervisor netcat-openbsd postgresql-dev gcc python3-dev musl-dev
 
 RUN mkdir /backend
 WORKDIR /backend

entrypoint.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 
 while ! nc -z db 5432; do sleep 3; done