[v1.9.x] Update Dockerfile.build.ubuntu_cpu_jekyll

ci/docker/Dockerfile.build.ubuntu_cpu_jekyll

@@ -16,54 +16,30 @@
 # specific language governing permissions and limitations
 # under the License.
 #
-# Dockerfile to build and run MXNet on Ubuntu 18.04 for CPU
+# Dockerfile to build MXNet main website
 
-FROM ubuntu:18.04
+FROM ruby:2.6.5-buster
 
 WORKDIR /work/deps
 
-SHELL ["/bin/bash", "-l", "-c" ]
-
-RUN apt-get update && apt-get install -y \
-      build-essential \
-      git \
-      zlib1g-dev \
-      wget \
-      gnupg2 \
-      curl
-
-# Always last, except here to prevent conflicts with rvm
-ARG USER_ID=0
-ARG GROUP_ID=0
-COPY install/ubuntu_adduser.sh /work/
-RUN /work/ubuntu_adduser.sh
-
-RUN curl -sSL https://rvm.io/mpapis.asc | gpg2 --import - && \
-    curl -sSL https://rvm.io/pkuczynski.asc | gpg2 --import - && \
-    curl -sSL https://get.rvm.io | bash -s stable
-
-RUN source /etc/profile.d/rvm.sh && \
-    rvm requirements && \
-    rvm install 2.6.3 && \
-    rvm use 2.6.3 --default
-
 ENV BUNDLE_HOME=/work/deps/bundle
 ENV BUNDLE_APP_CONFIG=/work/deps/bundle
 ENV BUNDLE_BIN=/work/deps/bundle/bin
 ENV GEM_BIN=/work/deps/gem/bin
 ENV GEM_HOME=/work/deps/gem
 
-RUN echo "gem: --no-ri --no-rdoc" > ~/.gemrc
-RUN yes | gem update --system
-RUN yes | gem install --force bundler
-RUN gem install jekyll
+RUN echo "gem: --no-ri --no-rdoc" > ~/.gemrc && \
+    yes | gem update --system && \
+    yes | gem install --force bundler && \
+    gem install jekyll
 
 ENV PATH=$BUNDLE_BIN:$GEM_BIN:$PATH
 
 COPY runtime_functions.sh /work/
 
-RUN chown -R jenkins_slave /work/ && \
-    chown -R jenkins_slave /usr/local/bin && \
-    chown -R jenkins_slave /usr/local/rvm
+ARG USER_ID=0
+ARG GROUP_ID=0
+COPY install/ubuntu_adduser.sh /work/
+RUN /work/ubuntu_adduser.sh
 
 WORKDIR /work/mxnet