Converting Dockerfile to use the alpine image

This matches the image used in .gitlab-ci.yml.

Pinning alpine:3.13 due to errors with gem install in 3.14.

.gitlab-ci.yml

@@ -2,7 +2,7 @@ stages:
   - test
   - deploy
 
-image: alpine:latest
+image: alpine:3.13
 
 variables:
   JEKYLL_ENV: production

Dockerfile

@@ -1,11 +1,19 @@
-FROM jekyll/builder
+FROM alpine:3.13
 
 WORKDIR /tmp
 ADD Gemfile /tmp/
 ADD Gemfile.lock /tmp/
-RUN bundle install --frozen
 
-FROM jekyll/jekyll
+RUN apk list -I && \
+    apk --no-cache add libatomic readline readline-dev libxml2 libxml2-dev \
+    ncurses-terminfo-base ncurses-terminfo \
+    libxslt libxslt-dev zlib-dev zlib \
+    ruby ruby-dev yaml yaml-dev \
+    libffi-dev build-base git nodejs
+RUN pwd && \
+    ls -l
+RUN gem install etc bundler --no-document
+RUN bundle install
 
 VOLUME /src
 EXPOSE 4001