please help while install the npm

[ivkris...@gmail.com]

1. A concise explanation of the problem you're experiencing.

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

npm WARN optional Skipping failed optional dependency /chokidar/fsevents:
npm WARN notsup Not compatible with your operating system or architecture: fsev...@1.2.4

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you're using, your operating system and browser.

[Mark Erikson]

The `fsevents` module is an optional dependency for some of the build tools that Cesium uses (I think it's Mac-only or something).  Per the message, this is just a warning, and not an error.  You can safely ignore it.