Add ruby2.3-alpine image

Dockerfile.ruby-2.3-alpine

+FROM ruby:2.3-alpine
+
+RUN apk -U add git make gcc g++
+
+# Set UTF-8 http://jaredmarkell.com/docker-and-locales/
+ENV LANG en_US.UTF-8
+ENV LANGUAGE en_US:en
+ENV LC_ALL en_US.UTF-8