Merge branch 'branch-0.3.1' into 'branch-0.3.1'

add helm stable repo

See merge request megasearch/milvus!191

Former-commit-id: 960e1fe7df0cc53c6caab981d1281332d0c14cd9

ci/jenkinsfile/deploy2dev.groovy

 try {
-    sh 'helm init --client-only --skip-refresh'
+    sh 'helm init --client-only --skip-refresh --stable-repo-url https://kubernetes.oss-cn-hangzhou.aliyuncs.com/charts'
     sh 'helm repo add milvus https://registry.zilliz.com/chartrepo/milvus'
     sh 'helm repo update'
     sh "helm install --set engine.image.repository=registry.zilliz.com/${PROJECT_NAME}/engine --set engine.image.tag=${DOCKER_VERSION} --set expose.type=clusterIP --name ${env.JOB_NAME}-${env.BUILD_NUMBER} --version 0.3.0 milvus/milvus-gpu"