THRIFT-1857 Python 3 Support
Client: Python
Patch: Nobuaki Sukegawa

Add py3 cross test
diff --git a/build/docker/centos/Dockerfile b/build/docker/centos/Dockerfile
index 8d5596a..2ba73c3 100644
--- a/build/docker/centos/Dockerfile
+++ b/build/docker/centos/Dockerfile
@@ -50,7 +50,7 @@
 RUN yum install -y ant junit ant-nodeps ant-junit java-1.7.0-openjdk-devel
 
 # Python Dependencies
-RUN yum install -y python-devel python-setuptools python-twisted
+RUN yum install -y python-devel python-setuptools python-twisted python-six
 
 # Ruby Dependencies
 RUN yum install -y ruby ruby-devel rubygems && \