bump ruby to 2.4.2

ruby/2.4.2/Dockerfile

@@ -0,0 +1,24 @@
+FROM debian:jessie
+
+MAINTAINER Ric Lister <rlister@gmail.com>
+
+RUN apt-get update && \
+    DEBIAN_FRONTEND=noninteractive \
+    apt-get install -yq \
+    build-essential \
+    zlib1g-dev \
+    libssl-dev \
+    libreadline6-dev \
+    libyaml-dev \
+    libffi-dev
+
+ENV RUBY_MAJOR_VERSION 2.4
+ENV RUBY_VERSION 2.4.2
+
+ADD http://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR_VERSION}/ruby-${RUBY_VERSION}.tar.gz /tmp/
+
+RUN tar -zxf /tmp/ruby-${RUBY_VERSION}.tar.gz && \
+    (cd ruby-${RUBY_VERSION} && ./configure --disable-install-doc && make install) && \
+    rm -rf /tmp/ruby-${RUBY_VERSION}.tar.gz && rm -rf ruby-${RUBY_VERSION}
+
+RUN gem install bundler --no-rdoc --no-ri