curl progress meter output to active-responses.log for ossec-slack.sh

[ocabj]

Whenever ossec-slack.sh sends a message to a given slack channel, the curl command in the ossec-slack.sh active response script will write the curl progress meter output to active-responses.log.

Not sure if this is intentional, but for a cleaner active-responses.log file, the -s / --silent will keep that meter from being written out. Although, that may silence a curl error / error in sending to slack.