Use jre instead of jdk

Author: cpuguy83

1.7/Dockerfile

@@ -1,7 +1,7 @@
-FROM java:8
+FROM java:8-jre
 ENV JRUBY_VERSION 1.7.18
 RUN mkdir /opt/jruby \
-  && curl https://s3.amazonaws.com/jruby.org/downloads/1.7.18/jruby-bin-${JRUBY_VERSION}.tar.gz \
+  && curl -sSL https://s3.amazonaws.com/jruby.org/downloads/${JRUBY_VERSION}/jruby-bin-${JRUBY_VERSION}.tar.gz \
   | tar -zxC /opt/jruby --strip-components=1 \
   && update-alternatives --install /usr/local/bin/ruby ruby /opt/jruby/bin/jruby 1
 ENV PATH /opt/jruby/bin:$PATH