Update samples' dependencies

samples/rest-notes-slate/slate/Dockerfile

@@ -2,19 +2,28 @@ FROM ruby:2.6-slim
 
 WORKDIR /srv/slate
 
+VOLUME /srv/slate/build
 VOLUME /srv/slate/source
+
 EXPOSE 4567
 
-COPY . /srv/slate
+COPY Gemfile .
+COPY Gemfile.lock .
 
 RUN apt-get update \
     && apt-get install -y --no-install-recommends \
         build-essential \
+        git \
         nodejs \
     && gem install bundler \
     && bundle install \
-    && apt-get remove -y build-essential \
+    && apt-get remove -y build-essential git \
     && apt-get autoremove -y \
     && rm -rf /var/lib/apt/lists/*
 
-CMD ["bundle", "exec", "middleman", "server", "--watcher-force-polling"]
+COPY . /srv/slate
+
+RUN chmod +x /srv/slate/slate.sh
+
+ENTRYPOINT ["/srv/slate/slate.sh"]
+CMD ["build"]