Add missing param

[GenoZhou]

Added missing parameter to resolve following error when building the image:

Total download size: 12 M
Is this ok [y/d/N]: Exiting on user command
Your transaction was saved, rerun it with:
 yum load-transaction /tmp/yum_save_tx.2018-01-29.02-48.J3a5Qm.yumtx
The command '/bin/sh -c rpmkeys --import file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
&& yum update&& yum install -y --setopt=tsflags=nodocs unzip libunwind libicu epel-release
&& rpmkeys --import file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
&& yum install -y --setopt=tsflags=nodocs leveldb-devel
&& yum clean all' returned a non-zero code: 1