Update Dockerfile

Install Yarn before bundling stuff

Dockerfile

@@ -1,5 +1,8 @@
 FROM ruby:2.5
 RUN apt-get update -qq && apt-get install -y nodejs postgresql-client
+RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
+RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
+RUN apt update && apt install yarn
 RUN mkdir /myapp
 WORKDIR /myapp
 COPY Gemfile /myapp/Gemfile
@@ -14,4 +17,4 @@ ENTRYPOINT ["entrypoint.sh"]
 EXPOSE 3000
 
 # Start the main process.
-CMD ["rails", "server", "-b", "0.0.0.0"]
+CMD ["rails", "server", "-b", "0.0.0.0"]