Add "2.0" as a supported version of Ruby (since upstream officially supports it with security updates)

2.0/Dockerfile

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+FROM buildpack-deps:jessie
+
+ENV RUBY_MAJOR 2.0
+ENV RUBY_VERSION 2.0.0-p481
+
+# some of ruby's build scripts are written in ruby
+# we purge this later to make sure our final image uses what we just built
+RUN apt-get update \
+	&& apt-get install -y bison curl ruby procps \
+	&& rm -rf /var/lib/apt/lists/* \
+	&& mkdir -p /usr/src/ruby \
+	&& curl -SL "http://cache.ruby-lang.org/pub/ruby/$RUBY_MAJOR/ruby-$RUBY_VERSION.tar.bz2" \
+		| tar -xjC /usr/src/ruby --strip-components=1 \
+	&& cd /usr/src/ruby \
+	&& autoconf \
+	&& ./configure --disable-install-doc \
+	&& make -j"$(nproc)" \
+	&& apt-get purge -y --auto-remove bison ruby procps \
+	&& make install \
+	&& rm -r /usr/src/ruby
+
+# skip installing gem documentation
+RUN echo 'gem: --no-rdoc --no-ri' >> /.gemrc
+
+RUN gem install bundler
+
+CMD [ "irb" ]

2.0/onbuild/Dockerfile

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+FROM ruby:2.0.0-p481
+
+RUN mkdir -p /usr/src/app
+WORKDIR /usr/src/app
+
+ONBUILD ADD Gemfile /usr/src/app/
+ONBUILD ADD Gemfile.lock /usr/src/app/
+ONBUILD RUN bundle install --system
+
+ONBUILD ADD . /usr/src/app