Three should be specified as a dependency

[gtg3vv]

This is similar to https://github.com/w3reality/three-geo/issues/13, but threejs is not listed as a dependency of this project even though it is used explicitly in index.js. Creating a new Threelet instance requires having THREE already be defined as the imported threejs module. This I assume is alright if the two scripts are included in sequence as in the example, but does not work when installing via npm as suggested in the readme.

index.js needs a line similar to import THREE from 'three' after listing it as a dependency