Add cesium packages to workspace.

Author: na9da

package.json

@@ -3,6 +3,8 @@
   "workspaces": {
     "packages": [
       "packages/terriajs",
+      "packages/terriajs-cesium/packages/engine",
+      "packages/terriajs-cesium/packages/widgets",
       "packages/terriajs-server",
       "packages/plugin-sample"
     ],