CentOS 7: Missing -y to yum update

docker/Dockerfile.centos7

@@ -2,7 +2,7 @@ FROM centos:7
 
 RUN groupadd -r mysql && useradd -r -g mysql mysql
 
-RUN yum update && yum install -y --setopt=tsflags=nodocs epel-release && \
+RUN yum update -y && yum install -y --setopt=tsflags=nodocs epel-release && \
     yum install -y --setopt=tsflags=nodocs which gcc make bison curl-devel \
     expat-devel flex hiredis-devel \
     jansson-devel json-c-devel libevent-devel libxml2-devel \