Container now have all proper dependencies (daattali#322)

Container was not working because didn't have all dependencies, and change CMD command for ENTRYPOINT.

Author: JosemyDuarte

Diff for: Dockerfile

@@ -2,12 +2,11 @@ FROM jekyll/jekyll
 
 WORKDIR /srv/jekyll
 COPY Gemfile .
+COPY Gemfile.lock .
 
 RUN gem install bundler
-RUN bundle install --clean --quiet
+RUN bundle install --quiet --clean
 
 EXPOSE 4000
 
-CMD [ "/usr/gem/bin/bundle", "exec", "/usr/local/bundle/bin/jekyll", "serve", "--port", "4000", "--host", "0.0.0.0" ]
-
-STOPSIGNAL 2
+ENTRYPOINT ["jekyll", "serve"]