update stressng install on RHEL

Author: johnkemnetz

articles/chaos-studio/chaos-studio-tutorial-agent-based-cli.md

@@ -66,7 +66,7 @@ sudo apt-get update && sudo apt-get -y install unzip && sudo apt-get -y install
 Or:
 
 ```bash
-sudo dnf -y install https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm && sudo yum -y install stress-ng
+sudo dnf -y install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm && sudo yum -y install stress-ng
 ```
 
 ### Enable chaos target and capabilities