Fix vfb example on geppetto-showcase

I'm seeing:
```
VFBExample.js:116 Uncaught (in promise) TypeError: three__WEBPACK_IMPORTED_MODULE_4__.Geometry is not a constructor
at VFBExample.get3DPlane (VFBExample.js:116:22)
at VFBExample.onMount (VFBExample.js:167:24)
at Canvas._callee$ (Canvas.js:82:5)
at tryCatch (Canvas.js:2:1)
at Generator._invoke (Canvas.js:2:1)
at Generator.next (Canvas.js:2:1)
at asyncGeneratorStep (Canvas.js:2:1)
at _next (Canvas.js:2:1)
```
When loading the vfb example on the geppetto showcase

Start in VFBExample.js at get3DPlane around line 116, then trace its call from onMount around line 167 and the Canvas.js stack entry around line 82. Reproduce the VFB example and inspect the Three.js geometry usage; done means the example loads without the reported Geometry constructor error.

Written by the indexing model from the issue text.