Dockerfile in ascii_binder-0.1.3.2 vs Dockerfile in ascii_binder-0.1.4

@@ -1,6 +1,7 @@
 FROM centos/ruby-22-centos7
 
+RUN scl enable rh-ruby22 -- gem install listen -v 3.0.8
 RUN scl enable rh-ruby22 -- gem install ascii_binder
 USER root
 RUN yum install -y java-1.7.0-openjdk && \
     yum clean all