Migrate ubuntu:18.04 -> alpine:3.8

Dockerfile

@@ -1,22 +1,22 @@
-FROM "ubuntu:18.04"
+FROM "alpine:3.8"
 LABEL maintainer="Julien Cabillot <dockerimages@cabillot.eu>"
 
-RUN export DEBIAN_FRONTEND="noninteractive" && \
-    export BUILD_PACKAGES="ruby-dev libxml2-dev" && \
-    export RUNTIME_PACKAGES="ruby" && \
-    apt-get -qq update && \
-    apt-get -qq --yes install ${BUILD_PACKAGES} ${RUNTIME_PACKAGES} && \
-    gem install foodcritic && \
-    apt-get -qq --yes remove --purge ${BUILD_PACKAGES} unzip zip fonts-lato javascript-common libjs-jquery  && \
-    apt-get -qq --yes autoremove --purge && \
-    apt-get -qq --yes clean all && \
-    rm -rf "/usr/share/doc/"* \
-           "/usr/src/"* \
-           "/var/cache/"* \
-           "/var/lib/apt/lists/"* \
-           "/var/log/"{apt/*,dpkg.log} \
-           "/tmp/"*
+ENV NOKOGIRI_USE_SYSTEM_LIBRARIES=1
 
-WORKDIR "/data"
+RUN apk --no-cache upgrade && \
+    apk --no-cache add ruby && \
+    apk --no-cache add --virtual build-dependencies \
+        build-base \
+        libxml2-dev \
+        libxslt-dev \
+        ruby-dev && \
+    echo 'gem: --no-document' > /etc/gemrc && \
+    gem install json foodcritic --no-rdoc --no-ri && \
+    gem cleanup \
+    apk del build-dependencies && \
+    rm -rf /usr/lib/ruby/gems/*/cache/* \
+        /var/cache/apk/* \
+        /tmp/* \
+        /var/tmp/*
 
-ENTRYPOINT [ "/usr/local/bin/foodcritic" ]
+ENTRYPOINT [ "/usr/bin/foodcritic" ]