migrate source Docker image to a debian based one, fixup dockerfile

Dockerfile

@@ -1,12 +1,13 @@
-FROM mcansky/base_ruby:2c7652fa95a2ab9419bb85e81a7c801ca6fa65d2
+FROM ruby:2.3.5-slim
+
+RUN apt-get update && apt-get install -y build-essential libffi-dev libgdbm-dev libncurses5-dev libreadline-dev libssl-dev libyaml-dev zlib1g-dev curl libyaml-0-2 libxml2-dev libxslt-dev
+#RUN apk --update add --virtual openssl-dev build-dependencies ruby-dev build-base
 
 # Set environment variables.
 ENV HOME /var/app
 ENV RACK_ENV production
-
 # Define working directory.
 ADD . /var/app
-
-RUN cd /var/app; bundle install
+RUN cd /var/app; bundle install --without development test
 
 CMD ["./var/app/bin/http"]

hello.rb

@@ -4,7 +4,7 @@ require 'redis'
 require 'sidekiq/api'
 require 'haml'
 
-$redis = Redis.new
+$redis = Redis.new(url: ENV['REDIS_URL'])
 
 class SimpleApp < Sinatra::Base
 

worker.rb

@@ -3,7 +3,7 @@ require 'sidekiq'
 require 'redis'
 require 'sidekiq/api'
 
-$redis = Redis.new
+$redis = Redis.new(url: ENV['REDIS_URL'])
 
 class SinatraWorker
   include Sidekiq::Worker