demo: Update GLTFLoader.js to latest three.js
demo: Update GLTFLoader.js to latest three.js

This incorporates upstream changes, notably the use of relative morph
targets and optimized bounding geometry. As a result this requires
three.js r111 to work fully (older versions will still work except for
morph targets).

zeux/meshoptimizer,zeux/meshoptimizer,zeux/meshoptimizer