use https for 3d tiles sample sever

How to use https for 3d tiles sample sever instead of http server?

Look at the changes in server.js and package.json here: https://github.com/AnalyticalGraphicsInc/cesium/pull/5317/files#diff-78c12f5adc1848d13b1c6f07055d996e

To run the server in http2 model: node server.js --http2

The code here is based off this guide: https://webapplog.com/http2-node/

Got it. Thanks!