var botId = "5ec0435908007b6b8cd85190b1";
function sendText(text){
  UrlFetchApp.fetch("https://api.groupme.com/v3/bots/post", {"method":"post", "payload":'{"bot_id":"' + botId + '","text":"' + text + '"}'})
}

function doPost(e){
  var post = JSON.parse(e.postData.getDataAsString());
  var text = post.text;
  var user_id = post.user_id;
  var name = post.name

  if (text.indexOf("changed name to") > -1 && user_id == 0)
     sendText("Welcome to Groupme");
}

function doGet(){}