Update Dockerfile comments wrt deprecation of Docker Toolbox

Dockerfile

@@ -6,15 +6,13 @@ MAINTAINER Marcin Kulik <support@asciinema.org>
 #
 #     docker run -d -p 5432:5432 -e POSTGRES_PASSWORD=mypass --name=postgres postgres
 #     docker run -d -p 6379:6379 --name=redis redis
-#     docker run --rm -e DATABASE_URL="postgresql://postgres:mypass@172.17.42.1/asciinema" foobarto/asciinema.org bundle exec rake db:setup
+#     docker run --rm -e DATABASE_URL="postgresql://postgres:mypass@postgres/asciinema" asciinema/asciinema.org bundle exec rake db:setup
 #     # starting sidekiq using the provided start_sidekiq.rb file will also start sendmail service if you don't want to use SMTP
 #     # otherwise start sidekiq by starting: bundle exec sidekiq
-#     docker run -d -e DATABASE_URL="postgresql://postgres:mypass@172.17.42.1/asciinema" foobarto/asciinema.org ruby start_sidekiq.rb
-#     docker run -d -e DATABASE_URL="postgresql://postgres:mypass@172.17.42.1/asciinema" -p 3000:3000 foobarto/asciinema.org
+#     docker run -d -e DATABASE_URL="postgresql://postgres:mypass@postgres/asciinema" asciinema/asciinema.org ruby start_sidekiq.rb
+#     docker run -d -e DATABASE_URL="postgresql://postgres:mypass@postgres/asciinema" -p 3000:80 asciinema/asciinema.org
 #
 # You can override the address/port that is sent in email with login token by passing HOST="host:port" environment variable when starting the web server.
-#
-# Assuming you are running Docker Toolbox and VirtualBox: go to http://192.168.99.100:3000/ and enjoy.
 
 ARG DEBIAN_FRONTEND=noninteractive
 ARG NODE_VERSION=node_6.x
@@ -115,12 +113,9 @@ COPY docker/supervisor/asciinema.conf /etc/supervisor/conf.d/asciinema.conf
 
 VOLUME ["/app/config", "/app/log", "/app/uploads"]
 
-# 172.17.42.1 is the docker0 address
-ENV DATABASE_URL "postgresql://postgres:mypass@172.17.42.1/asciinema"
-ENV REDIS_URL "redis://172.17.42.1:6379"
-# when using Docker Toolbox/Virtualbox this is going to be your address
-# set to whatever FQDN/address you want asciinema to advertise itself as
-# for ex. asciinema.example.com
+ENV DATABASE_URL "postgresql://postgres:mypass@postgres/asciinema"
+ENV REDIS_URL "redis://redis:6379"
+
 ENV HOST "localhost:3000"
 
 CMD ["/usr/bin/supervisord"]