Update yum epel mirror (#2547)

Signed-off-by: Nquicksilver <zhifeng.zhang@zilliz.com>

docker/deploy/cpu/centos7/Dockerfile

@@ -13,7 +13,9 @@ FROM milvusdb/milvus-dev:amd64-centos-7-core AS openblas
 
 FROM centos:centos7
 
-RUN yum install -y epel-release && \
+RUN yum install -y wget && \
+    wget -P /etc/yum.repos.d/ http://mirrors.aliyun.com/repo/epel-7.repo && \
+    yum clean all && yum makecache && \
     yum install -y libgomp libgfortran4 mysql-devel && \
     rm -rf /var/cache/yum/*
 

docker/deploy/gpu/centos7/Dockerfile

@@ -15,7 +15,9 @@ FROM nvidia/cuda:10.1-devel-centos7
 
 ENV NVIDIA_DRIVER_CAPABILITIES compute,utility
 
-RUN yum --disablerepo=cuda install -y epel-release && \
+RUN yum --disablerepo=cuda install -y wget && \
+    wget -P /etc/yum.repos.d/ http://mirrors.aliyun.com/repo/epel-7.repo && \
+    yum clean all && yum makecache && \
     yum --disablerepo=cuda install -y libgomp libgfortran4 mysql-devel && \
     rm -rf /var/cache/yum/*