Updating rails while working with Docker?

Question

I'm trying to update some gems including rails.

How can a run bundle install while working with Docker.

My Docker files looks like this:

 FROM ruby:2.4.1
 RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs
 RUN mkdir /myapp
 WORKDIR /myapp
 ADD Gemfile /myapp/Gemfile
 ADD Gemfile.lock /myapp/Gemfile.lock
 RUN gem install bundler --no-ri --no-rdoc && bundle install
 ADD . /myapp