Fix loki-install sed command

The current loki-install sed command in module 10 is not working, fixed it

Author: tonylixu

module10/loki-stack/readme.MD

@@ -20,7 +20,7 @@ cd loki-stack
 ```
 ### replace all `rbac.authorization.k8s.io/v1beta1` with `rbac.authorization.k8s.io/v1` by 
 ```
-sed -i s#rbac.authorization.k8s.io/v1beta1#rbac.authorization.k8s.io/v1#g *.yaml
+grep -rl "rbac.authorization.k8s.io/v1beta1" . | xargs sed -i 's/rbac.authorization.k8s.io\/v1beta1/rbac.authorization.k8s.io\/v1/g'
 ```
 ### install loki locally
 ```