CesiumJS 1.68 release

[Omar Shehata]

Hi everyone,

We're starting the CesiumJS 1.68 release. It will be out later today. Highlights include:

• Basic underground rendering support
• Source maps so you get more helpful error stack traces when debugging
• Support for editing shaders on the fly with SpectorJS

Full changelog: https://github.com/CesiumGS/cesium/blob/master/CHANGES.md#1680---2020-04-01

[Omar Shehata]

CesiumJS 1.68 is now out! Read about it plus all the big updates we've been working on for the past month on the blog here: https://cesium.com/blog/2020/04/01/cesium-april-release/