Fix to disable auto updates on rhel8 (#898)

diff --git a/packer/build-rhel-8.json b/packer/build-rhel-8.json
index 0f1f21e..c2acb6f 100644
--- a/packer/build-rhel-8.json
+++ b/packer/build-rhel-8.json
@@ -64,7 +64,7 @@
       "execute_command": "{{.Vars}} /bin/sudo -E -S bash '{{.Path}}'",
       "inline": [
         "yum update -y",
-        "yum remove -y df-automatic"
+        "yum remove -y dnf-automatic"
       ]
     },
     {