Bump to 1.7 .18

Author: cpuguy83

1.7/Dockerfile

@@ -1,5 +1,5 @@
 FROM java:8
-ENV JRUBY_VERSION 1.7.17
+ENV JRUBY_VERSION 1.7.18
 RUN mkdir /opt/jruby \
   && curl http://jruby.org.s3.amazonaws.com/downloads/${JRUBY_VERSION}/jruby-bin-${JRUBY_VERSION}.tar.gz \
   | tar -zxC /opt/jruby --strip-components=1 \