sh.zio.backup: change break for return

usr/local/bin/sh.zio.backup

@@ -73,10 +73,10 @@ function invoke_restic() {
 
     if [[ -z $command ]]; then
         say warning "No command specified. Not running"
-        break
+        return
     elif [[ $command == "generate" || $command == "self-update" ]]; then
         say warning "Unsupported command: $command"
-        break
+        return
     fi
 
     "$restic_path" \