add color to success output in slack

Jenkinsfile

@@ -60,4 +60,4 @@ parallel 'centos7': {
     }
 }
 
-slackSend "${env.JOB_NAME} #${env.BUILD_NUMBER} Complete (<${env.BUILD_URL}|Show More...>)"
+slackSend color: "#00ff00", message: "${env.JOB_NAME} #${env.BUILD_NUMBER} Complete (<${env.BUILD_URL}|Show More...>)"