Resolve bug when de zabbiz return 504 in html

[hallanneves]

I have problems with the timeout of zabbix. The sugestion of the solution is add this lines:

        try{
          JSON.parse(rawData);
        } catch{
          reject(new Error('Invalid content.\n' +
          `Expected json but received ${rawData}`));
          return;
        }
        resolve(JSON.parse(rawData));

In the file wrapper.js in the line number 89.

Best regrads.