Reduce docker image size (#394)

Reduce docker image size based on:  https://cadu.dev/reduce-your-docker-images-an-example-with-ruby/

docker/entrypoints/rails.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/bin/sh
 
 set -x
 
@@ -17,10 +17,9 @@ done
 
 echo "Database ready to accept connections."
 
-YARN="yarn check --integrity"
 BUNDLE="bundle check"
 
-until $YARN && $BUNDLE
+until $BUNDLE
 do
   sleep 2;
 done