Serve jekyll site with nginx

Dockerfile

FROM alpine:3.7 as build-env
MAINTAINER Jan Soendermann

# This list of packages was taken from the official jekyll image.
# Some of them are probably not required but since this is
# just a build env, it doesn't matter so much.
RUN \
  apk --update add readline readline-dev libxml2 libxml2-dev libxslt  \
    libxslt-dev python zlib zlib-dev ruby ruby-dev yaml \
      yaml-dev libffi libffi-dev build-base nodejs ruby-io-console \
        ruby-irb ruby-json ruby-rake ruby-rdoc ruby-dev
RUN gem install bundler -v 1.16.1 --no-document

RUN bundle config --global silence_root_warning 1
RUN echo "gem: --no-rdoc --no-ri" > ~/.gemrc

WORKDIR /jekyll
COPY Gemfile .
COPY Gemfile.lock .
RUN bundle install --jobs 3

COPY . .
RUN bundle exec jekyll build --destination /site

FROM nginx:1.15.0
COPY --from=build-env /site /usr/share/nginx/html
EXPOSE 80