Base docker image on alpine

Dockerfile

@@ -2,23 +2,22 @@
 # docker build -t transmission-rss --build-arg UID=1337 --build-arg GID=1337 .
 # docker run -it -v $(pwd)/transmission-rss.conf:/etc/transmission-rss.conf transmission-rss
 
-FROM ruby:latest
+FROM ruby:alpine
 MAINTAINER henning mueller <[email protected]>
 
 ARG UID=1000
 ARG GID=1000
 
 RUN \
-  useradd -m ruby && \
-  sed -i "s/1000:1000/$UID:$GID/" /etc/passwd && \
-  sed -i "s/1000/$GID/" /etc/group && \
-  chown -R ruby:ruby /home/ruby
+  addgroup -g $GID ruby && \
+  adduser -u $UID -G ruby -D ruby && \
+  apk --no-cache --update add build-base libffi-dev
+
+USER ruby
 
 WORKDIR home/ruby
-ADD . transmission-rss
-RUN chown -R ruby:ruby transmission-rss
+COPY . transmission-rss
 
-USER ruby
 WORKDIR transmission-rss
 RUN bundle