Fixed T1018, Remote System Discovery - sweep (#603)

The `-o` flag exists only for the MacOs ping command, it doesn't in the Linux (Ubuntu) command.

I just removed it, it should be necessary since it is already using `-c 1`.

atomics/T1018/T1018.yaml

@@ -69,7 +69,7 @@ atomic_tests:
     name: sh
     elevation_required: false
     command: |
-      for ip in $(seq 1 254); do ping -c 1 192.168.1.$ip -o; [ $? -eq 0 ] && echo "192.168.1.$ip UP" || : ; done
+      for ip in $(seq 1 254); do ping -c 1 192.168.1.$ip; [ $? -eq 0 ] && echo "192.168.1.$ip UP" || : ; done
       
 - name: Remote System Discovery - nslookup
   description: |